已知正四棱柱ABCD﹣A1B1C1D1中，AA1=2AB，E为AA1中点，则异面直线BE与CD1所形成角的余弦值为（ ）
—Let's play ping-pong.
—______.[ ]
A. No, I don't.
B. That sound interesting.
C. OK! It's boring.
D. I don't have a ping-pong bat.
新更换的炉管应与原炉管的材质相同。
