已知一个等腰梯形的下底与上底之差等于一腰长，则这个等腰梯形中的较小的角的度数为
A.30°
B.60°
C.45°
D.75°
答案：B
观察细胞分裂适宜选用的材料是（ ）
A．洋葱表皮细胞
B．洋葱根尖细胞
C．人的口腔上皮细胞
D．以上都可以
Simon _____ the photos when I came to visit him. [ ]
A. enjoyed
B. is enjoying
C. was enjoying
D. has enjoyed
