小华和小明每天坚持跑步,小明每秒跑6米,小华每秒跑4米,如果他们同时从相距200米的两地相向起跑,那么几秒后两人相遇?若设x秒后两人相遇,可列方程( ).
6x+4x=200
He told us that he ______ the letters in the morning.[ ]
A. will post
B. have posted
C. was posting
D. had posted
炎性腰背痛的特点有()
A.活动后症状改善
B.夜间痛
C.隐匿性起病
D.40岁以前发病
E.休息后症状无改善