下列哪种昆虫的发育过程要经过卵、若虫、成虫三个阶段（ ）

若关于 、 的二元一次方程组 $\{\begin{array}{c}3\text{x-}5\text{y=}2\text{a}\\ 2\text{x+}7\text{y=a-}18\end{array}$ 的解中x与y的值互为相反数，求 的值；

一种植物的特征是“无种子、有茎叶、有假根。”你认为这是（   ）

    In Britain, people usually begin their talks with____. For example, they will say” It's a fine day, isn't it?” “Do you____ it will rain?”

    Many people believe that they are____ to tell what the weather will be like. But they never____with each other. One man may say, “How cloudy (阴的) it is now! It's going to rain.”____ man will say, “No, it's going to be fine later.”

    People always hope the weather they want. For____, when a farmer needs water, he looks for something to tell him it's going to____. When a man wants to travel, he is sure the weather will be ____ quickly.

    Now almost everyone____ to the weather report. It doesn't always tell us the weather we want, it only tells us what the weather will be ____. But sometimes it makes mistakes(错误).

如图所示，物体S 在平面镜前，所成的像为S'。若在镜后AB处放一块不透明的塑料，则像S'将会 （  ）