__________ valuable advice it is. It will be of __________ great value to me.

What animals do you like —- I like __________.

Can you tell me how to learn English well? — Do more speaking, I think, ______ you will not be good at spoken English[ ]

Scientists are working hard to make possible for people to live on Mars in the future.

(2013·潍坊市高三二模)Sometimes smiles ________ be false, hiding other feelings like anger, fear or worry.