北半球哪一天各地昼最短,夜最长,北极圈以北地区出现极夜现象?
参考答案:北半球冬至日各地昼最短,夜最长,北极圈以北地区出现极夜现象。
在工具磨床上刃磨尖齿铣刀,需在磨头架上固定()
A.拨盘
B.卡盘
C.拨杆
D.齿托架
How long will it take experts to agree how to measure obesity().
A. Half a year.
B. One year.
C. One and a half year.
D. Two years.