中度有机磷杀虫药中毒时全血胆碱酯酶活性为( )
A.50%~30%B.30%~10%C.70%~50%D.以上均不确切E.90%~70%
参考答案:A
___________ you okay? [ ]
A. are
B. Is
C. Are
简述混播优缺点。