[单选题]
If you push twice as hard againstq)h,prf q5sm m ksm032 a stationary brick wall, the amount hq 3 eod6f s/czr0e:2fc*b 4wfof work you db3q0 rf6 / hc:f24s*wce oezfdo
A. doubles.
B. is cut in half.
C. remains constant but non-zero.
D. remains constant at zero.
