You can choose any movie, as long as it's not too scary.

as 在这里是连词，表示"当...时"或"因为"的意思。 long 本义是"长的"，在这里与as搭配构成固定短语。 as long as 是一个固定搭配的连词短语，意思是"只要"，表示条件或限制。