选C
not the slightest 一点也不...,丝毫都不...
用法请参考
1.There was not the slightest hint of trouble.当时看不出丝毫会出现麻烦的迹象.
2.There is not the slightest fear of rain today.今天一点也用不着担心会下雨.
3.Not the slightest sound penetrated the walls.一点声音也穿不过这道墙.
4.There is not the slightest doubt about it.关於那件事一点疑问也没有.
weakest 最脆弱,
thinnest 最薄
smallest 最小（体积）
都不能修饰doubt