问题补充：
【小题1】We will turn off the lights for an hour on Earth Day.(对划线部分提问)
When will What/ How about we turn off the lights for an hour?
【小题2】 Shall we have a picnic at the weekend? (改为同义句)
asked; to stop talking having a picnic at the weekend?
【小题3】“Will you please open the window?” she said to him. (将直接引语改为间接引语)
She that/ which cost him open the window.
【小题4】They kept on talking until the teacher came in. (改为同义句)
They didn’t until the teacher came in.
【小题5】 The new high-speed Hangzhou-Shanghai line started running last year. It cost about 29 billion yuan. (合并为含定语从句的句子)
The new high-speed Hangzhou-Shanghai line about 29 billion yuan started running last year.
答案：
解析：
【小题1】对时间提问用疑问词when，后跟一般疑问句，助动词will提前，故本题空格处填When will。
【小题2】本句是提出建议，也可以用what about或how about提出建议，后跟动名词，表示……怎么样的含义，故本题空格处填What/ How about。
【小题3】本句的含义为她叫他把窗户打开，ask sb to do sth表示叫某人做某事，故本题空格处填asked; to。
【小题4】本题的含义为也可以为直到老师进来的时候他们才停止说话，stop doing sth表示停止做某事，故本题空格处填stop talking。
【小题5】修饰名词高铁线为定语从句，先行词为物关系词可用that或which，本题表示过去，从句谓语动词用价值的过去式cost，故本题空格处填that/ which cost。
