已知A={1,2,3},B={x∈R|x2-ax+1=0,a∈A},则A∩B=B时,a=________.
1或2
验证a=1时B=满足条件;验证a=2时B={1}也满足条件.
I couldn’t get through the door because there was a big box ______.[ ]
A. by the way
B. on the way
C. out of the way
D. in the way
将下列结构与其相对应的主要功能用直线连接起来:
根 运输有机物、无机盐和水
茎 吸收水分和无机盐
毛细血管 气体交换
鳃 物质交换