US President Barack Obama ________ a national speech at the 10th anniversary of 9/11 terror attacks.[ ]

Researchers are now conducting hibernation experiment and can use chemicals to put living cells into sleep-like state_____ they don’t age.

m, what did you do this summer vacation—Guess what I had ______great fun in _______show performance “ Voice of China” .

The fire the death of twenty persons was caused by his carelessness.

It was the training ______ he had as a young man _____ made him such an excellent speaker.