The following are the common student groupings in classroom. Decide what way that the teacher group students in each situation. Put the right letter a-d in the brackets.It refers to the time when students work on an exercise or a task. It could be a dialogue reading, a game or an information-gap task between the two students.
选项：

A:Individual study;
B:Group work;
C:Pair work ;
D:Whole class work