1 . Mr. Green is still ____________(energy) though he is in his seventies. (所给词的适当形式填空)

2 . Not only is he hard-working but also he is ___________ (engergy). (所给词的适当形式填空)

3 . In order to work efficiently, experts suggest we should exercise more to keep__________.(energy)（所给词的适当形式填空）

4 . You should regularly work out so as to keep yourself _________ (energy) and thus work more efficiently. (所给词的适当形式填空)