2.Both texts are about relationships [there] are slowly breaking apart.该为that.这里是个定语从句
3.Being a forgetful teenager,she always[ lefts ]her gloves in the train and would lose her temper completely when her mother scolded her afterwards.该为left.left是leave的过去式,把.留在..
4.[ Under] our visit to London we talked all the time.该为on,on one's visit to 固定短语