A. 星型 B. 星型和链型 C. 星型、链型和环型 D. 星型、链型、环型和树型
A. it must have rained B. it must rain C. it must be raining D. it must have been raining
A. 拇指与食指 B. 拇指与中指 C. 拇指与无名指 D. 拇指与小指