从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
21．In _____ preparation for the launching of Shenzhou Ⅶ, scientists need ______ knowledge of weather changes.
A．the; the B．a; ∕ C．∕; a D．the; a
22．Some people are born with the belief _____ they are masters of their own while others feel _____ they are at the mercy of others.
A．what; that B．that; that C．that; ∕ D．∕; that
