Before sometimes, the monkey jumped . . . . . . the river. A. on B. into C. near D. upon

The correct answer is B. The monkey jumped into the river.

The other options are incorrect because they do not make sense in the context of the sentence. The monkey cannot jump on the river, because the river is not a solid object. The monkey cannot jump near the river, because the river is not a place. The monkey cannot jump upon the river, because the river is not a surface.

The word “into” is used to indicate movement from one place to another. In this case, the monkey is moving from the land to the river. The word “into” is the most logical choice for this sentence.