The Natural Approach teachers have three central roles: to be the primary source of comprehensible input in the target language, ______and to choose and use a rich mix of classroom activities.

A．to make learners active in class

B．to help learners understand messages

C．to create a classroom atmosphere that is interesting, friendly

D．to teach students grammatical rules

有以下程序：　　main( )　　{ int aa[4][4]={ {1，2，3，4}，{5，6，7，8}，{3，9，10，2}，{4，2，9，6} }；　　　int i，s=0；　　　for(i=0；i＜4;i++) s+=aa[i][1]；　　　printf("%d\n"，s)；　　}　　程序运行后的输出结果是（ ）。

A．11

B．19

C．13

D．20