"Provided" is the only correct answer. As well as meaning "as long as", it also means "under the condition that". Obviously, "although" and "unless" make no sense. "As" by itself is extremely unclear. Would it mean "because" or "while" in the sentence? Still, neither option makes sense. There's nothing unusual or rare about any of the words given. You simply need to know them if you do a Cambridge test.

#2 is correct and it is a natural sentence. It just rearranges the sentence. Imagine it this way: I'll take you skiing next weekend, provided you get your father's permission. "Provided" is a rare conjunction. Unless COULD work, but it probably is not something you would hear. It would make it sound like you are forced to go unless you get permission to not go. It isn't really natural.

Think of it this way: "provided" sometimes translates to "if." So: "If you get your father's permission, I'll take you skiing next weekend."

"Provided" is the answer I would choose. It is not listed, but I normally would say, "As long as you get . . . . " Both of these mean there is a condition that must be fulfilled before the second part of the sentence can happen. Although and as do not work. They make no sense in the sentence. "Unless" could work depending on context prior to the sentence, but "provided" seems to be the best answer in my opinion.

#2 is the only correct answer. If, as longs as, only if you get.....this is what it means in other words.