727.        The demand for airplane mechanics is expected to grow about ten percent a year in the next decade, largely because new federal rules calling for major modifications to older planes and because the airlines are adding hundreds of new jets.

(A) new federal rules calling for major modifications to older planes

(B) new federal rules, which call for major modifications to older planes

(C) new federal rules call for major modifications to older planes

(D) major modifications to older planes called for by new federal rules（C）

(E) major modifications to older planes are called for according to new federal rules

选 c, 为什么呢？

首先, 这个句子的主句是The demand... is expected to grow... ,because...

and because...
因而because从句 要是完整句子 ——  A 、B选项排除

D选项想表达被动语态, 缺be动词 are —— D排除

其次, call for 意思是 require, 所以主动语态优先, C优于E —— 排除E
因而 选择becasue...rules call for ... modification...