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3.1.teenagers and adults 

   2.children and adults

   3.children and teenagers

   4.teenagers and adults

children: under 12 years old

teenagers: from 13-18 years old

adults: 19 years old and up

4.1. need

   2.must 

   3.will

   4.should

   5.can

 Use 'need' to indicate necessary things

Ex: I need to learn how to swim.

 Use 'must' = 'bắt buộc' to tell others to do something

Ex: You must be quiet in the library.

 Use 'will'= 'sẽ' to express a choice or willingness

Ex: I will wake up early tomorrow.

  Use 'should' = 'nên' in an imperative sentence

Ex: You should brush your teeth every day.

  Use 'can' to show ability

Ex: He can drive a car.