常用来观察微生物的运动特征、分类鉴定的培养基的是（）培养基.
A.半液体培养基
B.液体培养基
C.固体培养基
D.半固体培养基
参考答案：D
237+238+239+240+241+242+243=______×______=______．
He didn't make________clear when and where the meeting would be held.[ ]
A. this
B. that
C. it
D. these
