We all jumped with joy at the exciting news, After all, we ______forward to the chance for many years.

A．are looking

B．were looking

C．have been looking

D．had been looking

最简单的透镜两个表面都是球面的一部分，通过两个球心的直线，叫做透镜的__________ ，如果透镜的厚度比球面的半径小许多，这种透镜又叫做__________ ，其中心O点叫做透镜的__________ 。