问题补充：
of the surface of the earth covered with water.
A. Seven-tens...are
BSeven-tens…is
CSeven-tenths...is
D. Seven-tenths...are
答案：
A. Seven-tens...are
B. Seven-tens…is
(答案→)C. Seven-tenths...is
D. Seven-tenths...are
解析：句意：地球表面的十分之七被水覆盖。分数的基本形式为分子为基数词，分母为序数词，分数视为一个整体，单数，故选C.
