a+(a-1)2=-2+(-3)2=-2+3=1．
-- ________ does your mother often run with her dog?
-- About half an hour.[ ]
A. How many
B. How long
C. How much
D. How old
超高层民用建筑设置的避难层（间），其净高不得低于（）。
A、1.5m
B、2m
C、2.5m
D、3m
f an hour.[ ]