英语中,“虽然”和“但是”不能在一句话里同时出现."因为"和"所以"也不能在一个句子中同时出现.
Although they are poor,they are friendly.他们虽穷却友善.但不能是“Although they are poor,but they are friendly.”
Because he didn't study hard,he failed in college.但不能是“Because he didn't study hard,so he failed in college.”