They ______ brothers. [ ]
A. are their
B. is their
C. are they
D. is they
答案：A
氨苄西林含量测定方法是
A．汞量法B．硫醇汞盐法C．四氮唑比色法D．HPLCE．GC
教师在教学中运用的直观教具可以分为两类：一类是实物直观，另一类是（）。
