A．connects
B．equivalent
C．experiences
D．experiments
E．figure
F．gradually
G．heartfelt
H．immediately
I．leave
J．powerful
K．proving
L．reluctant
M．strength
N．suppose
O．tools

A．They have lasted for only a short period of time.
B．They continue to play an essential role in teaching.
C．They can make students more active in study.
D．They have proved to be ineffective.