直线y=2x+1的参数方程是 ( )
A:x=t2y=2t2+1
B:x=2t-1y=4t+1
C:x=t-1y=2t-1
D:x=cosθy=2sinθ+1
下列四种现象中,只发生能的转移而不发生能的转化的过程是 ( )
- I'm tired. I want to have a day _________ next week.
- Great idea, honey. You do need a break.
如果按图中虚线对折可以做成一个上底面为无盖的盒子,那么该盒子的下底面的字母是____