(2013·高考新课标全国卷Ⅱ)Since nobody gave him any help，he________have done the research on his own.

The weather in the south is generally warm, but it________ be very cold sometimes.

 Whether dying patients      be helped to end their lives is a tough moral question.

--- That T-shirt with Yao Ming’s picture on it ________ belong to David. He admires him a lot.  ---No, it ________ be his. He hates black color. 

I ________ myself more— it was a perfect day.