(1) Mr. Brown wanted a yukata for his sister’s birthday present, because she always wanted him to send her something Japanese.
(2)Mr. Brown was surprised because the clerk gave him the yukata that she had bought for her mother.
(3)The clerk said so because when she was a high school student staying in Australia, the people were very kind to her.
(4)しかし、どの商品も欲しいものではなかったのです。
1~4なんですけど、because の前は省いても省かなくてもいいと思います!
でも作文を書く時は文をbecauseではじめない方がいいです。