直接引语中有情态动词must时变为间接引语时怎么变化？

如果表示推测的话就只能用must,表示“必须”一般情况下可以互换，但have to要变换时态，must不要，如果表示客观的必须的话，最好用have to，如果看不懂，看下面具体说明：

1）当must指过去时，如表不可推卸的义务，在间接引语里可以保持不变，也可用had to 代替。例如：
"I must warn you of the consequences," he said.
He told me he must/had to warn me of the consequences.

2）must说明将来的必要性是也可以保持不变， 或由 would have to 代替，有时亦可由had to 代替。例如：
"We must go early tomorrow," she said.
She said they must go early the next day.
She said they would have to go early the next day.
She said they had to go early the next day.

3）当 must被用来表推论或可能性时，在间接引语里也保持不变， 并且不可由had to 代替。例如:
"George must be a fool to behave like that," he said.
He said George must be a fool to behave like that.

4）must have, could have这样的形式（包括可用的否定形式），在间接引语里均保持不变。例如:
"I must have slept through the alarm," she said.
She said she must have slept through the alarm.

虽然比较抽象，但运用起来没有那么难的，希望我的回答能给你一些帮助。

变为had to

用have to