The Clarks haven't decided yet which hotel ( ) because there are many to choose from.

不定式前可以加某些疑问代词（who，what，which...）、疑问副词（when，where，how，why...）或连接词whether，构成特殊的不定式短语，如 what to do next， which one to choose， where to go， how to get there 等，在句子中作主语、宾语等成分，可排除选项B、D。stay作“暂住，逗留”讲时是不及物动词，其后跟宾语时应加介词，且介词不可省略，所以空处应用 to stay at，which hotel作介词 at的宾语。