屁股沟: cleft of the buttocks sulcus posteriorposterior rugae
因为: because; for; on account of 短语和例子只是因为... simply because ...; 不仅仅是因为 ... not merely because ...; 就因为他们钱挣得比我们多, 他们就认为高人一等。 just because they make more money than we do, they think they're so
