get down to （靜下心來）認(rèn)真處理 （工作等）,開始認(rèn)真注意 （細(xì)節(jié)等）.
e.g.After Christmas I'm going to get down to some serious job-hunting.
圣誕節(jié)后,我打算開始認(rèn)真的找工作.
get down to 里面的to 應(yīng)該是介詞,后面跟動(dòng)詞的ing形式.有點(diǎn)像look foward to 里面的to,都是介詞,后面都需要跟動(dòng)詞的ing形式.
get down 后面不跟 to do.
get down 表示漸漸的使某人不快,疲倦
All this waiting and delay is really getting her down.
get sth.down 表示記下,寫下（尤指某人說的話）
好像沒有set about to do的用法,但是有set about
set about 表示開始,著手做某事,可以說set about doing sth.表示開始（著手）做某事,尤其指費(fèi)事,費(fèi)勁的事.
She set about clearing up after the party.
聚會(huì)之后,他開始收拾東西打掃衛(wèi)生.
set out to do 表示為達(dá)到某個(gè)結(jié)果而開始做某事,著手進(jìn)行計(jì)劃.
She deliverately set out to poison her husband.
她蓄謀毒殺她的丈夫.
它們之間的區(qū)別,你就可以在解釋當(dāng)中明了了.謝謝你。非常感謝。^_^ 只是期待能有一個(gè)人來幫助我。That's OK! I hope you can improve your English by using dictionary. All the answers can be looked up in a dictionary. That is easy! :)