My pen pal Andrew found it difficult Chinese well.
A:learning
B:learn
C:to learn
设f(x)=x+2,(x≥0)1,(x<0),则ff(-1)=( )
“冲动是魔鬼,冲动是炸弹里的火药,冲动是一种吃不完的后悔药”这句话告诫我们在意志品质方面要增强( )