用显微镜对光时，如果视野内光线较强，应选择下列哪项来进行调节？（  ）

①较大的光圈      ②较小的光圈      ③反光镜的平面      ④反光镜的凹面．

 Some people still live in their hometown. However, others may only visit ____  once or twice a year. Millions of Chinese leave the countryside ____   (search) for work in the cities. Among these is Hua Xing. He  ____  (live) in Wenzhou for the last 13 years. With a hard job ____  a factory, he seldom visits his hometown. "I haven't been back for three years. It's  ____  (shame),”he says____   (develop) have been good in Hua Xing's hometown since 2002, for example, new roads____  (appear). A new school  ____   (build). However, some things will never change in his hometown. The big old tree is still beside the playground. Children in his time  ____   (usual) liked to play together under it. It was  ____ happy childhood.

将一根牛的腿骨纵剖开，观察到骨松质和骨髓腔内的骨髓均为红色，据此可判断这头牛是（　　）

如下图为某地等高线示意图，B点此时的温度为18℃，如果只考虑高度因素，那么甲峰与乙峰的温度分别为（    ）