if it's too soft, the tunnels will collapse, that's why this material cannot be too soft.
C: soft enough so it causes collapse: opposite meaning. We say 'My GMAT score is high enough to get me admitted by Stanford'. We don't say: 'My GMAT score is low enough to get my ass kicked by Standford adcom'
Besides, C is not so //:
so hard as to make .... or soft enough so it causes...: 不平行啊
-- by 会员 Kb24 (2011/4/25 17:44:56)