The sentence is generally saying that the specific area of land gives you shelter from a storm, which is basically safety. The word 'encloses' itself emanates safety, because basically, 'encloses' means to close over, or to surround. If you don't find that trapping, it would seem more safe than anything else, along with what the sentence itself is trying to say.
As for #5, I can't seem to view the full choices for the question. Could you maybe add another attachment, or list the other two choices there are?
The subordinate clause is "When the delivery man arrives" because 1. it is introduced by "when" and 2. we can ask question to the main clause about this one.
