A:蛙的口腔上皮细胞
B:蚕豆的叶肉细胞
C:蛔虫的受精卵细胞
D:人的神经细胞
配伍题(请将下列左侧内容与右侧内容进行合理搭配。)
He began to __________ because every means _______ tried already.