Study and learning 29.4 answer

1.It depends on what country they live.
2.6 years.
3.Teachers can know whether the students take their class hard.
4.The student might become passive in class.
5.The learner can contact with English at home.
6.Conducting many meanings of the words.
7.The former teach academic things.
  The latter teach technical things about the job they want to.
8.The former is incoherent.
  The latter has unity.