это не то, что я искала. есть что нибудь другое

1. i must brush my teeth. - anyone, most likely some disobedient child.

2. i have to brush my teeth. - a patient of dentist's, a human with diseased tooth.

3. i must tidy my room. - anyone, most likely some disobedient child.

4.i have to tidy my room. - anyone, probably a child.

5. i must take the medicine. - someone with easy form of illness.

6. i have to take the medicine. - most likely, a regular patient

a - have been

b - have not had. saw 

a - was

b - left. came. have found/ 

it's not always easy for the old and the young to find a common language.

это правильное утверждение, так как все люди разных возрастов жили в разное время. у более пожилых людей существуют свои стереотипы, также и у молодёжи. но всё-таки нужно стараться искать общий язык с пожилыми людьми, потому что они наши предки и знают намного больше нас. 

this is a correct statement, because all people of all ages living in different times. the older people have their own stereotypes, and young people too. but we must try to find a common language with the elderly people, because they are our ancestors and know far more than we do. 

pack of cigarettesa day -about 500x-rayirradiationfor the year! temperatureof 700-900degreessmoldering cigarette! smoker's lungswith the experience -black,rottingmass.afterinhalingnicotine enters thebrainin 7seconds.nicotinecauses spasmof vessels,fromheremalnutritionoxygen to tissues.spasmof small vesselsmakes the skinaging.the hazards of smokingin the factthatthere isbad breath, yellowteeth,inflamedthroat,eyesturn redfrom theconstant irritationof smoke.