题干
He didn't say anything because he felt sad at the bad news. (改写)
____ ____ at the bad news, he didn't say anything.
答案(点此获取答案解析）
Feeling,sad
是平面，给出下列命题： ①若
；②若
； ③若
； ④若a与b异面，且
相交； ⑤若a与b异面，则至多有一条直线与a，b都垂直.