India, Pakistan and China have border problems . . . . . . . . them.

Solution (By Examveda Team)

In the sentence, "India, Pakistan, and China have border problems . . . . . . . . them," the appropriate preposition is "between" when referring to issues involving two or more entities. Therefore, the correct completion is, "India, Pakistan, and China have border problems between them."

Therefore, the correct answer is Option B: between.