某金属单质跟一定浓度的硝酸反应，假定只产生单一的还原产物.当参加反应的单质与被还原硝酸的物质的量之比为2：1时，还原产物是（）

A.NO2

B.NO

C.N2O

D.N2

Some of the objectives of the Grammar-Translation Method are（） and to train a better understanding of the first language.

A. to help students read literature

B. to make students exercise move

C. to provide students with good mental exercise

D. to have learners listen and speak more