通读全文，理解大意，从各题所给的选项中选择可填入短文的最佳选项。

Nowadays, millions of Chinese leave the countryside to search for work in the cities. They usually go back to1once or twice a year. Zhong Wei is one of them.

Zhong Wei has lived in Wenzhou for the last 13 years. With a hard job in a crayon factory, he is too busy to find2to visit his hometown.

Many people like Zhong Wei regard with great interest 3their hometowns have changed. Perhaps large hospitals and new roads have appeared. In many places, the government has also built 4and sent teachers from the cities to help.

ZhongWei thinks such development are very good, and these changes will take place in his hometown because some things need to change in order to become 5.

He also thinks among all the changes, some things are6to change, such as the soft and sweet memories of the hometown in people's hearts. That is why people try to find time to go back to visit their hometowns though they are very busy.

①自然条件下，基因重组通常发生在生殖细胞的形成过程中；

②非同源染色体上某片段的移接，仅发生在减数分裂过程中；

③同卵双生兄弟间的性状差异是基因重组导致的；

④基因中一个碱基对发生改变，则生物的性状一定发生改变；

⑤在镜检某基因型为AaBb的父本细胞时，发现其基因型变为AaB，此种变异为基因突变．

根据图示，补全对话。

—____ do they talk about?

— They talk about a toy____.

I have a____.

【榜样故事】

2016年最美孝心少年许卓婧，6岁时母亲突患乳腺癌，变故让本来就不富裕的家庭变得更加艰难。爸爸是长途车司机，常年在外出差，妈妈选择了在家保守治疗。许卓婧看着病重的妈妈、劳累后变瘦的爸爸，她主动承担了买菜做饭、洗碗洗衣、照顾妈妈的重担。为了不影响孩子学习，妈妈想把女儿送到外婆家住，但是许卓婧坚决要留在家里照顾妈妈，她学习成绩优秀，在班里总是帮助其他同学。沉浸在音乐世界中的许卓婧总是积极乐观，他正在学习谱曲，5岁开始学习小提琴，每天晚上不管多累都要练琴，2015年她在全国少儿小提琴独奏展演活动中获得金奖。她希望将来能够成为一名小提琴家，想给妈妈写一首曲子，想用琴声帮助妈妈早点好起来。