nobody gave him any help, he ______ have done the research on his own

Don’t you think the weather is becoming hotter and hotter year by year—Yes. I think it’s one of __________ problems in the world these years.

____ nearly all behavior is learned behavior is a basic assumption of social scientists.

You can drive my car now, I had it ____yesterday morning.

tadium is very splendid and attractive in appearance, may be imagined.