It was with great joy _____ he received the news that his lost daughter had been found. [ ]

A. because

B. which

C. since

D. that

生态系统中能流的效率公式是( )。

A．同化效率＝固定的太阳能/吸收的太阳能(植物)

B．同化效率＝摄取的食物能/同化的食物能(动物)

C．生长效率＝营养级的同化量/营养级的净生产量

D．生长效率＝营养级摄取的食物能/营养级的净生产量