_____ is known to us is that the 2012 Olympic Games will take place in London．

Just like fingerprints, each person’s DNA is ________ unless he has a twin.[ ]

It is not always easy for the public to see _______ use a new invention can be of to human life.

Mum _____ to us, “Be quiet! Your sister is sleeping.”

What we learn today in school will ______ whether we can meet our challenges in the future.