Confusion in the usage of Preposition

[Millie]

A. Is it right that prepositions can only be followed by noun, gerund or possessive case?
B. Or only some prepositions can be put directly in front of clauses?

I feel quite confused as I know prepositions such as for and about can lead clauses directly. Is there any rules for this usage?

Thanks in advance!

[Mister Micawber]

.
A. Yes, but that includes noun clauses
B. I think most of them can, but I don't have the time to try.
.
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Native English teacher at Mister Micawber's