英语问题1.区分in/at/by the end2.是in a speed 还是 at a speed?3.China

英语问题
1.区分in/at/by the end
2.是in a speed 还是 at a speed?
3.China has built a great green wall _____ the northern part ____ the country .
A .to in B . across of C .across on D .at of
顺便解释一下
4.this shirt looks good ____ you
A .on B .up C .at D .after
解释?
5.-____ you ! -thanks !
A .after B.before C.with D.to
这句话什么意思啊