can someone whose read stephen king’s essay “now you take bambi or snow white - that’s scary!” tell me what strategies he uses?

The sentence that contains a dangling modifier is C. Having fallen behind the sofa cushion, I couldn't find my car keys for almost an hour.

A dangling modifier is an ambiguous sentence in which the reader is not sure what the modifier modifies. In this case, grammatically speaking, "having fallen behind the sofa cushion" is modifying "I" when the intended meaning was, probably, that the keys had fallen behind the sofa cushion and that is why the writer could not find them for an hour.