地壳的主要化学成分以（）、S、Al、Fe、Ca、Na、K、Mg、H等为主，这些元素占地壳总容量的98.13%
参考答案：O
Not only China but also other countries _____ trying to develop their own economy.[ ]
A. is
B. are
C. has
D. be
--- _______ is the train station from the school?---About twenty-minute bike ride.
A．How many
B．How long
C．How far
D．How soon
