AIDS is said_______ the biggest health challenge to both men and women in the earth over the past four years.

I haven’t seen her ____ the time ____ she had the accident.

I was just _______to go out when the telephone rang ．

______ Marx's works with Engels', and you'll find many differences．

.The President said to the public, “________ hoped that people in the area will recover from the terrible earth quake soon.”