Cho mình hỏi tại sao k.2.pi lại là tập con của k.pi? Mà ko phải ngược lại?

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chia động từ tổng hợp: 1/ they (correspond).................at least once every three months 2/ my sister (lie)..................on the beach at the moment 3/ my friend and i (be)...................pen pals since last year 4/ for a long time the aodai (be)......................the subject of poems, novels and songs 5/she (take)...............her friends to hoan kiem lake yesterday 6/ in the 1990s the world economic situation (get)...........worse 7/ would you like (come)................and visit me next summer? 8/ i (look) .............foward to (meet)....................my old friend now 9/ it (seem).................very difficult for me (have)................a trip abroad 10/ i suggest (tie)............the roof to the ground with pegs and ropes because there must (be)...........strong wind blowing 11/let's (practice)................(listen)..........english by (visit)...............thí web 12/ he (wish)..........he (know) ..................many friends 13/ i (wish)............i (can go)................to the cinema with you 14/if the rice paddies (pollute)..............,the rice plants will die 15/if all pollution (go)............on, the field (litter)...........with plastics and tins 16/ if i became rich, i (travel)....................................around the world 17/ he is short. if he (be) ...............taller, he (be) ....................able to join the pollice 18/ you used to (live)....................in los angeles, (do).............you? 19/you didn't watch tv last night, (do).........................you? 20/ my brother learns music well, (do).............he? 21/ the material, (call)....................jean,(name)..................after sailors 22/the word "jean"(come).................from a kind of material that (make)..............in europe 23/english must (improve)..................at school 24/she said that she (go)............to quy nhon the following day 25/ my father asked me if i (visit)................my brother in that city 26/my father (live)...............in quy nhon since i (be)..............born there 27/ ba (invite)..............liz (join)...........his family to the country two years ago 28/he (try) ............(answer )...................my questions quickly