Dear Michael, What a wonderful day it is today! The sun was always shining，but it was cool．I had a great field trip to East Mountain with Grandpa and Danny．The mountain was a little h
make an effort take in catch fire ever since，have a bad effect on，little by little end up 71. Working very hard, he is making progress _______________. 72. We met ten years ago and
，地球表面g=
，所以g′=
=2π
=
T。所以摆钟分针在此行星上走一圈的时间实际为
小时，B正确。