buy的用法给某人买：
buy sth for+钱 :买某物花了多少钱。I bought the book for 50 yuan.
buy sth for sb=buy sb sth 给某人买某物：He bought me a new coat. =He bought a new coat for me. 他给我买了一件新外套。
buy sth from sb（for+钱）（花了多少钱）从某人那里买了某物：
I bought it from a friend for ?0. 我从朋友那里花10英镑买来的。
sell的用法：
sell sb sth =sell sth to sb 卖给某人某物： He sold me the bike. =He sold the bike to me.他把自行车卖给我了。
sell sth for +钱：某物卖了多少钱；sell sb sth for+钱 =sell sth to sb for+钱：以多少钱把某物卖给某人：
He sold the bike for 100 yuan. 他的自行车卖了100元。
He sold me the bike for 100 yuan. =He sold the bike to me for 100 yuan.他以100元把自行车卖给了我。
sell（不及物动词） for+钱：卖了多少钱： The bike sells for 100 yuan. 这辆自行车卖100元。
sell （不及物动词）well畅销，卖得好：The book sells well. 这本书很畅销。
sell sth out：某物卖完了：The book has been sold out.这本书已经卖完了。
sell (sth) at a/the price of…以……价格卖（某物）：He sold the TV set at the/a price of 500 yuan.他以500元的价格把电视机卖了。
come across sb
不期而遇某人
something happen to sb
某人遇到某事
happen to meet sb or run across sb.碰巧遇到，不期而遇。
see sb ,meet sb 见到某人
meet with sth 碰到某事
come across sb /sth
happen to meet sb or run across sb.碰巧遇到，不期而遇。
see sb ,meet sb 见到某人
meet with sth 碰到某事
meet with
meet
happen to meet