S7. Students of different abilities are placed together in a cooperative learning groups in that________.

A．They detect nerve impulses transmitted to a grasshopper’s legs.
B．They sense how far a grasshopper has jumped.
C．They detect changes in air pressure.
D．They help a grasshopper find food.

A．The professor is old.
B．The professor is lazy.
C．The professor is sick.
D．The professor is only tired.