输送静脉血的血管是[ ]
A．肺动脉和主动脉
B．肺静脉和上、下腔静脉
C．肺动脉和上、下腔静脉
D．肺静脉和主动脉
答案：C
____________ is it from China to Canada? [ ]
A. How many
B. How far
C. How much
You can make a ______ by turning off the light after you leave the house.
A．difference
B．decision
C．promise
D．mistake
