下列估测与事实最接近的是 ( )
A.完整播放一遍我国国歌的时间约为 50 s
B.一本九年级物理课本的质量约为 25 g
C.家用电冰箱一天消耗的电能约为 24 kW · h
D.初中生小美站立在水平地面上对水平地面的压强约为 500 Pa
She often practices _____ on weekends.( )
sing
sings
singing
to sing
Although they feel tired,_____ they still go on working.( )
and
but
so
/
It isn't easy for us ______ English well.( )
learn
learns
learning
to learn
Who cleaned the room?
Li Lei _________.( )
is
was
dose
did
The man is feeling much better now,so you ______ call a doctor.( )
needn't
can't
mustn't
shouldn't