【单选题】计算以下10个玉米果穗长度(cm)( 19、21、20、20、18、19、22、21、21、19)的平均数和标准差为:
【单选题】Which animal is probably the original source of virus?
【单选题】若|2000x+2000|=20×2000,则x等于( )
【简答题】What is the original source language for each of the words provided? 所给词汇源于何种语言?
【单选题】What is the original source of tidal energy?
B.
The gravitational pull of celestial bodies
C.
Nuclear reactions within the Earth
D.
The Earth's rotation on its axis
【单选题】This smoke signal has passed its expiry date,and become damp and ineffective
A.
This smoke signal is damp but still effective
B.
This smoke signal is not damp but not effective
C.
This smoke signal is expired but still effective
D.
This smoke signal is expired and not effective