题型:选择题 He made a gesture by having his fingers ______. [ ]A. crossing B. cross C. crossed D. to cross 查看答案
题型:单项选择题 A1/A2型题 氟离子选择电极法中,使用的离子强度缓冲液通常含有醋酸盐,其pH为()。A.4.5~5.5B.5.0~5.5C.5.5~6.0D.6.0~6.5E.6.5~7.0 查看答案