Question

You have to tell the __________ .

Answer 1

You have to tell the truth.
你必须讲实话
tell the truth讲实话

Answer 2

You have to tell the reason /truth / result.

Answer 3

分析：
根据句意，tell后面填的是名词。
结论就是：
填：reason理由/truth真相/result结果/story故事/teacher老师/problem问题。