Recently some scientists have concluded that meteorites found on Earth

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1. The passage is primarily concerned with

Before going to the options, we should fairly get an idea of the primary point of the author. The crux of the passage is in the below sentence
"This conclusion has led to another question: whether meteorite impacts on Earth have similarly driven rocks from this planet to Mars."

Lets move to the answer choices -

(A) presenting an argument to support a particular hypothesis

Nothing about a hypothesis. Passage is clearly mentioning the whole thing as a question. A incorrect[/color]

(B) suggesting an answer to a theoretical question

Yes exactly, it is a question that a theoretical one as astronomer is just speculating. B Correct

(C) questioning the assumptions of a research project

Nothing about a Project. Passage is clearly mentioning the whole thing as a question. C incorrect

(D) criticizing experimental results

Nothing about any Experiment. Passage is clearly mentioning the whole thing as a question. D incorrect

(E) explaining the origin of certain scientific data

Nothing about Scientific data. Passage is clearly mentioning the whole thing as a question. E incorrect

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2. According to the passage, which of the following events may have initiated the process that led to the presence on Earth of meteorites from Mars?

Okay, so the important phrase in the question is - 'presence on Earth of meteorites from Mars'. We find a direct reference of this in the 3rd and 4th line of the passage -
"Martian origin might actually have been blasted free of Line Mars's gravity by the impact on Mars of other meteorites."

(A) A meteorite struck the Earth with tremendous velocity.

Does not match with the lines mentioned above.A incorrect

(B) A meteorite collided with Mars.

Can be deduced from the above set of lines B Correct

(C) Approximately 1,000 rocks were ejected from Mars.

Does not match with the lines mentioned above.C incorrect

(D) The orbits of Earth and Mars brought the planets to their closest points.

Does not match with the lines mentioned above.D incorrect

(E) Rocks from a meteorite impact broke free of Earth's gravity.

Does not match with the lines mentioned above.E incorrect

*** In these type of questions, better to find the relevant points in the passage rather than jog through your memory. The answers are written in such a way that it might just confuse you on data points after a quick read of the passage.***

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3. The passage suggests that which of the following is true concerning the probability that a rock, if ejected from Mars, will hit the Earth?

The only place where probability is mentioned is in the following lines -
"Phinney estimates that the probability of these rocks hitting Mars is about one-tenth as great as that of Mars's rocks hitting Earth."
Now if we read the question carefully it asks us about the probability of rock hitting from Mars to Earth and not the other way around as mentioned in the lines. So keeping this in mind lets see out answer choices -

(A) The probability is increased when particles are ejected from Mars in random directions.

No mention / reference of this option in given relevant lines.A incorrect

(B) The probability is increased by the presence of large craters on the surface of Mars.

No mention / reference of this option in the given relevant lines.B incorrect

(C) The probability is decreased when Mars's orbit brings the planet close to Earth.

No mention / reference of this option in the given relevant lines.C incorrect

(D) The probability is greater than the probability that rock from Earth will hit Mars.

Yes, this is what we were talking about. D Correct

(E) The probability is less than the probability that a rock from Earth will escape Earth's gravity.

No mention / reference of this option in the given relevant lines.E incorrect

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4. Which of the following, if true, would cast most doubt on Phinney's estimate of the probability of Earth rocks hitting Mars?

This question is on similar lines as question 3. So the answer will also be around those lines -
"so Phinney estimates that the probability of these rocks hitting Mars is about one-tenth as great as that of Mars's rocks hitting Earth. To demonstrate this estimate, Phinney used a computer to calculate where 1,000 hypothetical particles would go if ejected from Earth in random directions. He found that 17 of the 1,000 particles would hit Mars."
Okay, so after understanding this, lets read through the options

(A) Rather than going in random directions, about 25 percent of all particles ejected from Earth go in the same direction into space.

Probably yes, will mark if no better option present

(B) Approximately 100 meteorites large enough to make a noticeable crater hit the Earth each year.

This is based out of some other data point in the passage(irrelevant here. so we can eliminate at this point) and is not correct as well. 'Noticeable' is a subjective word. It can be anything between 1% to 99%. But in the para a definite value is given (]60 miles crater). Hence we can eliminate this option

(C) No rocks of Earth origin have been detected on Mars.

This does not cast doubt rather strengthens the astronomer's estimates. Hence can be eliminated

(D) The velocity of ' rocks escaping from Earth's gravity is lower than the velocity of meteorites hitting the Earth.

No direct of velocity anywhere in the relevant lines. Moreover no mention of it in the passage itself. Hence can be eliminated

(E) No craters more than 60 miles across have been found on Mars

Craters on Mars have not been talked about in the relevant lines. Hence can be eliminated
Hence A
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