CR -- rapidly.correctly get the test points

Dear zoezhuyan,

How are you, my friend? I'm happy to respond.

It's fine that you grouped three CR here. In the interest of time, I think I will respond to only one at a time.

There are a several factors going on here. GMAT CR are real world arguments, and the more you can have a sense of real world arguments, the more it would help you. See this blog:
GMAT Critical Reasoning and Outside Knowledge
Reading real world arguments, in newspapers and news journals, would help you develop good instincts for arguments. I know you have less than a month to your GMAT and you want to achieve a high level of master. I would say, that, in addition to all the GMAT-specific preparation you are going to do, you need to read & analyze so many real world arguments that you become a walking encyclopedia of issues in the modern business world. All GMAT CR arguments are designed so that if you have some familiarity with the real world issues, it will help you get the answer.

Now, this first question about breakfast cereals is essentially biological. It would help to do some science reading, for example in Scientific American, if you don't have a science degree in your undergrad. Nevertheless, unless you were familiar with the specific topic of the biology of vitamin assimilation in the human digestive system, it would be hard to have any outside knowledge that would help you.

Here's the prompt again, without your comments and by sentence:
1) Many breakfast cereals are fortified with vitamin supplements.
2) Some of these cereals provide 100 percent of the recommended daily requirement of vitamins.
3) Nevertheless, a well-balanced breakfast, including a variety of foods, is a better source of those vitamins than are such fortified breakfast cereals alone.
Sentences #1 & #2 are purely factual, and both contain breakfast cereals. These two facts seem to indicate that we can get all the vitamins we need from fortified breakfast cereals.
Sentence #3 is a radical change in direction. It upsets the expectation created by the first two sentences. This is a paradox question, because it creates expectations then changes them. It's the job of a paradox to create a certain amount of confusion, so you are hardly to blame if you found the prompt a bit confusing. In a way, that's the point. The prompt presents a paradox, and the answer choices will resolve it.

I will point out that on GMAT CR strengthen or weaken questions, it's often easy to predict the answer right after reading the prompt, but on a paradox question, it's usually hard or impossible to predict the prompt. Usually we just have to go through the answer choices. I think, after the prompt, you had the basic right idea: what makes the well-balanced breakfast better than the fortified cereals? Why does the former provide us with more vitamins with the latter if the latter contains all that we need?

(A) In many foods, the natural combination of vitamins with other nutrients makes those vitamins more usable by the body than are vitamins added in vitamin supplements
what I got is the breakfast with vitamin , nutrients seems include lot of , vitamin is one of this, I think of it as exaggerate -- cross off,
I'm not totally sure I understand what you were communicating about your reasoning here. There is no exaggeration here. This simply says that, for whatever reason, the vitamins from the well-balanced breakfast gives us vitamins that are "more usable by the body."
Well-balanced breakfast ==> body can use the vitamins well
Fortified cereals ==> body can't necessarily use all the vitamins that are there.
This is a valid reason why a well-balanced breakfast would provide more vitamins than would fortified cereals.

For (C), I would say this is tricky. The GMAT doesn't like "must" when we are drawing conclusions or assumptions or inferences or some kind of reasoning, but in terms of a purely factual statement about the world, "must" is fine.
Chinese citizens who want to live and work in the US must get a visa.
A person must go through several years of medical school to become an MD.
A car with plenty of gas that doesn't even turn over [url]must[/url] have a mechanical or electrical problem.
Those are factual true statements. Choice (C), in attempting to resolve a paradox, is providing another factual statement that contains the word "must," so we must accept this the way we would accept evidence. The word "must," by itself, is absolutely no reason to reject (C).

Choice (E) compares fortified cereals to cereals that haven't been fortified. These latter are not discussed in the prompt at all.

I think part of the problem is the phrase "a well-balanced breakfast." This is a phrase that is culturally understood in the USA. It means a breakfast that has food from different food groups. For example, when I think of a "a well-balanced breakfast," I would think of
1) eggs or French toast
2) some source of grain (whole wheat toast or cereal)
3) lots of fresh fruit
That's a big breakfast with different kinds of food. The eggs provide some categories of nutrients, and the fruit provides very different nutrients. That's what is meant by "a well-balanced breakfast." Choice (E) is comparing one kind of cereal to another. No single cereal, by itself, would constitute "a well-balanced breakfast."

This is part of what makes (A) stand out. (A) talks about "many kinds of food," which calls to mind the variety that must be in "a well-balanced breakfast."

You see, GMAT CR depends on the connotations of phrases such as "a well-balanced breakfast." The phrase has a very specific meaning in the mind of American speakers, and this meaning is crucial for the question. The only way you can get a sense of all the possible phrases that could show up is to develop a habit of reading. See:
How to Improve Your GMAT Verbal Score
You are going to be very busy preparing for the GMAT in the next month.

Does all this make sense?

Take very good care of yourself, my friend!

Mike