It is well known that nature has provided Shangri-la(香格里拉) with endless natural treasures, making the land happy home for the local people．

The girl _____ the US is my son’s English teacher. [ ]

I find this Math problem very ______. I believe students can work it out ______.

I have __________ written my composition, but she hasn’t __________.

The mobile phone has influenced people’s life a lot since it .