Believe it or not, that is _______ we have dreamt about for twelve years.

The traditional view is ______ we sleep because our brain is “programmed” to make us do so.

After the successful launching of the Shenzhou 9, ______ the astronauts will work and live in Tiangong-1— the space lab module is ______ the whole nation care about.

The boss believed Tom's reason for being late for work is ______ he had to help his grandma cook.

Water，which seems so simple and common，is________makes life possible.

Is this research center _________ you met some foreign guests last week?

The South Pole isn’t _____ people could find a comfortable place to live, for the average winter temperature there is below-40℃.

I'm afraid he’s more of a talker than a doer, which is ____ he never finishes anything．  

You are saying that everyone should be equal, and this is ______ I disagree.

---I’ll ask the teacher about past tense. I’m very puzzled about it.
--- That is just _____ most of our classmates have doubt.
what        B. why       C. where       D. how