Don't open the door. It's cold. Please ____ the door.
在数列{an}中,an+1﹣an=2,a2=5,则{an}的前4项和为( )
半干旱地区多是草原牧区,湿润半湿润地区多是农业区,这反映地理环境影响区域的( )
关于经纬线的叙述,不正确的是( )