I feel it hard to keep up with my classmates in study and sometimes I lose heart. But whenever I want to          ,

my teacher always encourages me to work harder. [ ]

A. go on

B. run away

C. give up

D. look out

二级中误差公式为（）。

A.0.02+0.0006S

B.0.01+0.0003S

C.0.02+0.001S

D.0.04+0.003S