Present tense and present perfect - impossible?

Having amassed is a modifier that modifies the Neuroscientists. You can place the entire modification before the subject, Having amassed......, Neuroscientists are now ......

I do have a particular question re the use of tenses on one question explanation: (OG 2017, #219):

all - thanks for the feedback but, as stated above, I am not interested in the correct solution but I am interested in the official explanation why the answer D is not correct.

Hi guenthermat, on the contrary, it is perfectly fine to combine present tense and present perfect. For example, following is a valid sentence:

I do not have any money because I have lost my wallet.

I do not have any money is simple present, while I have lost my wallet is present perfect. In fact, I cannot think of a better way to articulate this sentence.

The sentence that you've posted here however, is not strictly present tense; it uses present participle (in option D). This is what's creating bit of a problem here, because present participles of this type (that appear towards the end of a clause and are preceded by a comma) are supposed to depict a continuum and not discreteness.

For example, following would not be correct:

Michael has prepared hard for the exam, now planning to appear in the exam.

Again, the issue is that preparation has already been done (one discrete event) and his act of planning to appear in the exam is another discrete event. So, continuum is again missing and we cannot use present perfect here.

A better sentence would be:

Michael, having prepared hard for the exam, is now planning to appear in the exam.

p.s. Our book EducationAisle Sentence Correction Nirvana discusses participles, their application and examples in significant detail. If someone is interested, PM me your email-id; I can mail the corresponding section. In fact, this very sentence has been cited in our book.

It's possible! There's no rule against combining different tenses in the same sentence, as long as the sentence makes logical sense that way.

For instance, this is a logical sentence:

I bought a gallon of milk and will drink it this week.

And this is an illogical sentence:

I drank a gallon of milk and will buy it this week.

You could construct both logical and illogical sentences using present/present perfect, as well. For instance, this is logical:

Now that I have taken over the world, I look forward to the future.

But this is illogical:

Before I have eaten breakfast, I must do the dishes.