右下图为某森林生态系统物质循环示意图,请据图回答:
生态系统碳的吸收主要是通过()作用实现的,碳的释放主要是通过()作用实现的。
参考答案:光合作用;呼吸作用
This is my school. There are many trees and flowers in it. It’s very beautiful. The teaching building is big and tall. There is a big playground in our school. After 4:30 in the afternoon, many students come to the playground to play football and some students play table tennis in the table tennis room. There are 1,200 students and 25 classes in our school. The students all like to study. The teachers in our school are very good. They help the students to study and the students like them, too.
小题1:The school looks _____.
A.small
B.old
C.nice
D.bad小题2:The school is beautiful because of (因为) ________ in it.
A.trees and flowers
B.a playground
C.students and teachers
D.the table tennis room小题3:There are at least (至少) _____ students in one class.
A.50
B.45
C.75
D.65小题4:After class the students often go to _____.
A.their classroom
B.their homes
C.the playground
D.the teachers’ office小题5:Do the students like to study?
A.Yes,they do.
B.No,they don't.
C.Yes,they are.
D.No,they aren't.
如图所示,一物体恰能在一个斜面体上沿斜面匀速下滑,设此过程中斜面受到水平地面的摩擦力为f1。若沿此斜面方向用力向下推此物体,使物体加速下滑,设此过程中斜面受到地面的摩擦力为f2。则
A.f1为零,f2为零
B.f1为零,f2不为零
C.f1不为零,f2为零
D.f1不为零,f2不为零