A.If he studied more
B.If he were studying to a greater degree
C.Studying more
D.Had he studied more

A.impress
B.impressive
C.impression
D.impressionist

A.had looked cautiously before
B.looked with cautioned after
C.was looked cautious when
D.looks cautious when

A.at-on
B.in-for
C.on-for
D.over-for

A.take over
B.result in
C.hold on
D.keep to

A.that
B.whom
C.which
D.who

A.although
B.because of
C.in spite of
D.because

A.have I seen
B.have you seen
C.if I had seen
D.if had I seen

A.hadn’t wasted
B.didn’t waste
C.hasn’t wasted
D.wouldn’t waste

A.Nồng độ hoocmon sinh dục biến động theo chu kì
B.Các nhân tố bên trong biến động theo chu kì
C.Điều kiện môi trường biến động theo chu kì
D.Hoat động của hệ nội tiết biến động theo chu kì