-xx-y=x-x+y=xy-x.
故选A.
the situation become worse, call me at once.
A.Must
B.Need
C.May
D.Should
采用特制的干粉吸人装置,由患者主动吸入雾化药物的制剂是().
A.溶液型气雾剂
B.乳剂型气雾剂
C.喷雾剂
D.混悬型气雾剂
E.吸入粉雾剂