绿色植物能够释放二氧化碳，这和细胞中的哪个结构关系密切？（　　）

A．细胞膜

B．细胞质

C．叶绿体

D．线粒体

—The passage is too hard to understand.

—Yes, ________ it's very short and there are no new words in it.

A．so

B．as

C．because

D．though