Hi,
—What fruit is in season now? —Pears and apples, __________. A. I know B. I think C. I see D. I feel the answer is B. What about A? Is that ok here?
No, choose B. It's a very standard way of stating an opinion.
( I'd say —What fruits are in season now?
or perhaps 'What kind of fruit is in season now? )
Best wishes, Clive