It seemed to me as if nothing would or could ever be known. all that had so long engaged my attention suddenly grew despicable.
what change has the character experienced? he no longer enjoys his work.
he has gained a new appreciation for his work.
he has become closer with this friends.
he has taught something to his friends.

 He no longer enjoys his work.

In this excerpt, the speaker tells us that everything that he had previously been interested in suddenly became horrible to him. It is likely that the work the speaker was engaging in stopped being interesting or enjoyable for him. Moreover, he states that he began to feel as if nothing would or could ever be known. Therefore, it seems that the source of his frustration is that the speaker wanted to find out the truth of something, but now believes that it cannot be known.

. a function is a relation in which each input has only one output. in the relation , y is a function of x, because for each input x (1, 2, 3, or 0), there is only one output y. x is not a function of y, because the input y = 3 has multiple outputs: x = 1 and x = 2.

i would say a because the main idea is what the author is the point the author is trying to get across.