According to the previous question, where is it? Is it? Bob. It is inferred that the next sentence "He is reading in the library" is going on, so the present continuous tense is used. The present continuous tense consists of: the present participle of the subject +am/is/are+ verb; In the third person he, the subject is singular, the be verb is is, and the present participle of read is reading. So the answer is B.