下面对有关实验和探究的叙述不正确的是[ ]

A．探究动物的绕道取食，选择的实验动物越大越好

B．观察蚯蚓时，保持其体表湿润有利于它的体壁呼吸

C．用显微镜的低倍镜观察小鱼尾鳍内的血液流动

D．探究菜青虫的取食行为可用其他叶片做对照，如芹菜叶、菠菜叶等

The dog may be a good companion for the old. _______, the need to take it for walks may be a disadvantage.

A．Besides.

B．However

C．Therefore

D．Instead.