1.顺便拜访
2.B.when可以指时间点或者时间段,由when引导的时间状语从句,主句用过去进行时,从句应用一般过去时
3.C.not until指直到……才……,后面的Chinese people took on a new look缺少了时间状语,用when
4.converse指交谈,不及物动词,protect指保护,及物动词.你应该想问conserve和protect之间的区别吧.
（下面是转载网上的详细解答）protect用作及物动词,意为“保护,保卫,防护”（to keep someone or somthing safe from harm,damage,or illness),用于使人或物免受任何危险、侵袭或伤害,适用范围广泛.
如：protect one's country,(one's sister,one's head,the townspeople,one's interest)等,并常用protect...from 结构.
如：Try to protect your skin from the sun.
A helmet protects your head from injuries.
He raised his arm to protect his child from hurting.
conserve一般说保护自然资源,是指通过有准备、有计划的、明智的方法来保护事物处于安全,防止改变或损坏,如保护人等的权利,义务等
We must conserve our forests if we are to make sure of a future supply of wood.
如果我们想确保未来的木材供应,就必须保护森林.
"People have to learn to conserve water anytime,especially during the drought."
"大家必须学会节约用水,特别是在干旱期间."