Question

9. Not knowing        ，the host is having a headache in making the decision of selling his house. (stay)

不知是走还是留，主人正在为卖不卖房伤脑筋。

Answer 1

9. whether to leave or stay / whether / if he should go or stay考查"疑问词+不定式"结构和whether 的用法。whether to do sth.是否做某事。该结构可作主语、宾语和表语。knowing后缺宾语，而if (是否)不可接不定式，所以给出上述答案。