i dont get why 'contend'

But contend indeed means to fight or battle.

Here the scientist cast a hypothesis...............

Hope this helps

Contend is one of those tricky 2 definition words. Many native english speakers have probably heard the context used for the second definition regularly enough to know it, but non-english first language speakers might not have. While the first definition is something like "to deal with" such as you would contend with an opponent in a battle, the second definition is "to assert or claim," such as saying you contend that the color blue is better than red or you contend that smoking e-cigarettes is bad for you.

This blank uses the second definition. "To claim" and "To make a hyopthesis" are the most similar meanings available and thus the answer is D, F.

Contend: assert as a position

Ok Let me clear about this question

Basically the question itself conveys the following meaning

The scholars THINK, MAKE a hypothesis that certain fish are very sensitive BEFORE an earthquake and eventually sound the warning

The only pair of choices that fit the bill are D and F

Contend means ARGUE or make an assumption or hypothesis.

Contend= hypothesis

The others are irrelevant

Hope now this is clear

Hi Carcass, how about a "question", it is similar to "hypothesize", isn't it?

here the scholars think about a possible HYPOTHESIS, an idea to verify via observation or empirical data.

They DO NOT question or ARGUE anything, whatsoever.

I hope now is more clear.

I know what you mean: my question is why do the fish are sensitive ?

but asking a question is different from formulating a possible explanation.

Let me know if you need further explanations or clarifications