扩句。

①汉斯来到王宫前。

②骑着公鸡的人来。

    Do you know Chen Yixun? He is a great singer from Hong Kong. He has a lot of beautiful songs, so many people love him. This year Chen Yixun gives concerts (演唱会) in some cities in China. And on November 7 the concert is in Jiaxing.

    Chen Yixun wants to give great concerts, and he does a lot of work for that. First, he practises singing every day. And he always drinks warm water. There are also dances at the concerts, so he needs to practice dancing, too. It's a hard job. Then, he also needs to do exercise like running and swimming. He has to be healthy and strong for the concerts.

    “I have a busy life, but I love it. I enjoy singing and I wish to give great shows to people,” says Chen Yixun. Wish him good luck!

如图所示，让一束太阳光通过挡光板的夹缝照射到三棱镜的一个侧面上，用光屏接收到从三棱镜的另一侧出射的光线．

（1）实验时，一边慢慢转动三棱镜，一边注意观察光屏，在光屏上可观察到彩色光带，这说明____ ．

（2）如果分辨不清光屏上彩色光带的色彩，可以适当____ （选填“增大”或“减小”）光屏与三棱镜间的距离．

（3）光屏上A、B是彩色光带边缘的色光，其中B为____ 光，用温度计测试不同区域内光的热效应时，为了使它的示数变化更明显，改进措施是____ ．

函数$f\left(x\right)=x^3+a{x}^2+3x-9$，已知$f\left(x\right)$在$x=-3$时取得极值，则a=（   )