Помогите с вопросами по английскому

Question

1) when we came into the hall they _ discussing this problem? 
1. are 
2.were 
3. was 
 
2)since the time of Dalton, knowledge of chemistry ___ advanced greatly 
1.was 
2.had 
3.has 
 
3)D.i . Mendeleyev ____ his first description of the Periodic system in March of 1869. 
1) has published 
2)publish 
3)published

что то ответы расходятся

Денис Белоусов · Accepted Answer

1 were 
2 had 
3 has published

Ната Графичева · Answer

1. а 
2. в - результат актуален на настоящий момент, а не на какой-то момент в прошлом -- ставим перфект презент 
3. в - указан момент времени в далёком прошлом, ставим паст симпл

Ольга Корноухова · Answer

1) When we came into the hall, they were discussing this problem. 
2) Since the time of Dalton, knowledge of chemistry has advanced greatly 
3) D.I. Mendeleyev published his first description of the Periodic System in March 1869.

Михаил Убирия · Answer

1)were 
2)has 
3)published