A low-carbon lifestyle is of great benefit to improve _____ world environment. Nothing can

be enjoyed from it until you have____ deep understanding of it, though. [ ]

A. a; the

B. /; a

C. the; /

D. the; a

由同种不锈钢制成的饭锅、饭盒、小勺，根据公式ρ=m/V，可以得出的结论是（　　）

A．锅的质量大，所以饭锅的密度大

B．饭盒的体积比小勺大，所以饭盒密度比小勺小

C．小勺的体积小，所以小勺的密度大

D．饭锅、饭盒、小勺体积不同，它们的密度相同