骨骼肌中间较粗的部分叫____，两端较细的呈乳白色的部分叫____．
By the time I reached home , my parents ____ the dinner for me already
星系是宇宙中的一大群____、气体、尘埃等组成的系统，宇宙中的星系大约有1000亿个以上，银河系以外的星系称为____．
If you are planning to spend your money having fun this week, better ________ it—you've got some big bills coming.
