甲、乙两颗人造地球卫星围绕地球做匀速圆周运动,它们的质量之比m1:m2=1:2,它们圆周运动的轨道半径之比为r1:r2=1:2,下列关于卫星的说法中正确的是( )
We are going to celebrate the 100th anniversary of the founding of the Communist Party of China _________ July 1st,2021.( )
A.inB.onC.atD.of
—Tom,turn off the tap.Don't leave it running.
— .( )
A.Better notB.Sorry,I will
C.Not at allD.You' re welcome
Keep on dancing,and you'll be better at it. .( )
A.Practice makes perfect
B.Burn the candle at both ends
C.It never rains but it pours
D.A friend in need is a friend indeed
Tomorrow is Earth Day.Let's discuss .( )
A.when shall we give out the leaflets
B.what we can do to recycle things
C.how should we save more energy
D.whether can we make our city greener
David Attenborough 40 documentaries over the past 67 years.A Life on Our Planet is his latest work.( )
A.makesB.madeC.has madeD.is making