It is a simple sentence.
A simple sentence contains one independent clause - which is the case with sentence 7. There is one subject (they) and one verb (rule), which means that it is a simple sentence (because of one verb only). A dependent clause wouldn't be able to stand on its own, and sentence 7 obviously can, which is why it is not dependent.
The rooms were cool and restful
looks good to me:-) :-) :-) :-)
I believe C would be correct
