Use the required form of the infinitive after must: you must (to be) right," i said. they must (to hear) that the fellow was in london. but at last he rose realizing dully that he had work which he must (to do). he had a faint feeling of satisfaction in the thought that mait must (to wonder) why they had gone off together. 8.1 must (to sit) there for a quarter of an hour waiting and thinking about it before i saw the letter. 9. "his relatives do not think so." "then they must (to be) a lot of damned fools." 10.mrs cromwell took us round the yacht. there was no doubt that it must (to cost) her a lot of money. he had said that he himself was an admirer of stendahl. this must (to influence) him in making his decision. at half past two i heard hudson grunt, put down his book and switch out the light. he must (to read) since midnight. "i must (to get) old," she said, "to be talking like that." there were a lot of mirrors that must (to buy) at the sale of some old restaurant. when i jumped up the thing fell off my knee. it must (to lie) there yet.

You must (be) right," I said.
They must (have heard) that the fellow was in London.
But at last he rose realizing dully that he had work which he must (be done).
He had a faint feeling of satisfaction in the thought that Mait must (have been wondering) why they had gone off together.
I must (have been sitting) there for a quarter of an hour waiting and thinking about it before I saw the letter.
"His relatives do not think so." "Then they must (be) a lot of damned fools." Mrs Cromwell took us round the yacht. There was no doubt that it must (have cost) her a lot of money.
He had said that he himself was an admirer of Stendahl. This must (have influenced) him in making his decision.
At half past two I heard Hudson grunt, put down his book and switch out the light. He must (have been reading) since midnight.
"I must (be getting) old," she said, "to be talking like that."
There were a lot of mirrors that must (have been bought) at the sale of some old restaurant.
When I jumped up the thing fell off my knee. It must (be lying) there yet.