Put in 'can', 'can't', 'could' or 'couldn't'. if none of theses is possible use 'be able to'in the correct tense!1.i looked everywhere for my glasses but I ...... find them anywhere

2.she's seven years old,but she...........read yet. her parents are getting her extra lessons

3.i read the book three times,but I.........understand it.

4.my grandmother........... use a computer until last month.since then she's been taking lessons at the library.

5.i.......... understand the chapter we had to read for homework.it was so difficult.

6.i ....... lift this box - it's too heavy!would you help me?​