用异羟肟酸铁反应检识香豆素时,反应条件为()
A.碱性
B.先碱性,后酸性
C.酸性
D.先酸性,后碱性
E.中性
参考答案:B
Mr. Smith's doctor suggested him_______ cold food these days. [ ]
A. not eat
B. not eating
C. not to eat
D. didn't eat
火灾自动报警系统施工时,从接线盒.线槽等处引到探测器底座.控制设备.扬声器的线路,当采用金属软管保护时,其长度不应大于()m。
A.0.5
B.1
C.2
D.2.5