The Eiffel Tower weighs about_.A.700-ton heavy B.700-ton-heavy C.700 tons D.700-ton
问题描述：
The Eiffel Tower weighs about_.A.700-ton heavy B.700-ton-heavy C.700 tons D.700-ton
答
B 这是数名形（数词 名词 形容词）的复合形容词.因为有连字符,所以不用变复数.如果这题你不明白,我再给你举个例子,道理一样的.
The girl is about six-year-old.这也是复合形容词哩~
有问题再追问.