Why not use “which” instead of “what“? —-> He pulled the cloth off what looked like a pie.”
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Best answer
"What" is an interrogative pronoun while "which" may be used as interrogative pronoun or a relative pronoun. In the sentence "He pulled the cloth off which looked like a pie.", "which" is a relative pronoun used as the subject of the relative clause "which looked like a pie". This relative clause is used as an adjective clause modifying the noun "cloth". Better say "He pulled the cloth which looked like a pie off." or "He pulled off the cloth which looked like a pie."
- John Kenmuir(AKA John Connor) Cambridge certified teacher since 1998, former IELTS speaking examiner
To put it simply, you can't (use "which" instead of "what") in this sentence. In "He pulled the cloth off what looked like a pie", the dependent clause "what looked like a pie" is the object noun. If you replace "what" with "which", the dependent clause "which looked like a pie" is an adjective phrase, not an object noun. You'd have to include an object noun before "which" in order to make a proper sentence. The result would be "He pulled the cloth off the ________ which looked like a pie" (and "which looked like a pie" would describe the missing word "_______").