1 hasn't called
2 bought
3 hasn't returned
4 How long has she known about this problem?
5 Have you ever heard such an unbelievable story?
6 have lived
7 has bought
8 I have always wanted one
M(N):m(оксида)=63,6:100
m(N):m(O)=63,6:36,4
это по массе, а нам надо перейти к количеству n(N):n(O)=63,6/14:36,4/16
4,5:2,275=2:1
N2O
1 writer ( писатель)
2 icy ( ледяные)
3 homeless( бездомные)
На, тут усе просто, вроде)
On our dacha site we have a garden.