The conference had been held to discuss the effects of tourism ___ the wildlife in the rainforest.
He __________ sleep, although he tried to, when he got on such a hunt for an idea until he had caught it.
-You needn't take an umbrella. It isn't going to rain.-Well, I don't know. It __________ do.
It __________ be the vocabulary that caused you the problem in the exercise because you know a lot of words.
No one __________ be more generous; he has a heart of gold.
-Why are your eyes so red? You __________ have slept well last night.-Yeah, I stayed up late writing a report.