不属于被覆黏膜的是()
A.牙龈
B.颊黏膜
C.唇黏膜
D.硬腭
E.舌背黏膜
参考答案:A, D, E
从一个新鲜的紫色洋葱表皮细胞来看,组成原生质层的是
①细胞壁 ②细胞膜 ③细胞质 ④液泡膜 ⑤液泡 ⑥细胞液[ ]
A.①②③
B.②③④
C.③④⑤
D.②④⑥
Some people thought ________ possible to live on out space in the future .
A.it
B.it be
C.it is
D.that is