题目

The fact has worried many scientists ______ the earth is becoming warmer and warmer these years. A. what              B. which             C. that              D. though 答案：C(’06贵州)一间普通教室内空气的质量大约是(空气密度约为) [　　] A．3.0kgB．30kg C．300kgD．3 000kg