某兴趣小组为农民设计了冬季生态型种植养殖模式，如图所示，请根据图回答下列问题：

（1）牛通过______作用产生的二氧化碳可进入蔬菜大棚，蔬菜在光照条件下，利用二氧化碳进行______作用，合成有机物；

（2）稻草除了作为牛的饲料外，还可与牛粪混合进行发酵，参与发酵的微生物在生态系统的成分中被称为______，能够把有机物分解为______；

（3）生态系统的能量流动和物质循环是沿着______进行的，能量流动的特点是______．

If you _____ at school, you _____ a college student now. [ ]

A. had studied hard; would have been

B. should have studied hard; should have been

C. had studied hard; would be

D. would study hard; must have been