A:①②
B:①③
C:②③
D:②④
如图,将三角形纸片ABC沿DE折叠,使点A落在BC边上的点F处,且DE∥BC,当DE=2时,BC的长为( )
下列有关限制酶的叙述中正确的是
人体产生血细胞的部位是( )
This is my new teacher, Mr. Chen.
____
I saw him a large box in his hands and enter the room.