I would go for the A.
In C it seems odd to put in the who and use the gerund just behind.

I would say A. E does not seem right for the following reason: To estimate the age of the oceans one will divide "ocean's current salt levels" A by "the resulting increase in salt levels in the oceans over the past hundred years" a . Whether or not "the salts carried into th...

My answer would be B. C does not seem consistent because of: "Have bothered" on its own (for me) indicates past. If you add "did" on it you are putting another indicator of past atop. In my opinion, a better formulation for C could be: (C) however, caffeine does not seem to have ...

(A) Her claim that animal experimentation is justifiable if it supports human values contradicts her claim that such experimentation is justifiable only if it leads to cures for human ailments. The two do not contardict each other but they are simply not in the same direction of reasoning. In her fi...

You got "such firms" at the end of the sentence. That presupposes the firms were evoked somewhere before in the sentence. So I would go for E which is the only answer talking about the firms.

Are you okay with that?

I would go for C