A:what; that
B:that; which
C:that ; what
D:what; which
我国社会主义初级阶段经济制度的基础是( )
①点燃酒精灯;②加热;③用试管夹夹好试管;④往试管中加入2-3mL食盐水;⑤将试剂瓶盖好,放回原处.