It is obvious that on no account _____ to the teacher that he has done the homework on his own.

A．this is the first time he is lying

B．this is the first time he has lied

C．is this the first time has he lied

D．is this the first time he has lied

某钢筋混凝土粱的跨度为9m．当设计无具体要求时．混凝土强度满足（）时方可拆除底模。

A.≥50％设计强度

B.≥75％设计强度

C.≥100％设计强度

D.保证混凝土表面及棱角不因拆除而受损坏