Выберите правильную букву
1. Scientist and engineers … developing the ways to reduce the acidity of rains since the beginning of this century.
A) are C) have been B) has D) will have
2. The sulfur dioxide … already … greatly to acid formation.
A) contribute C) are contributing B) has contributed D) contributed
3. They informed that there … suggested a 5% reduction of sulfur dioxide.
A) has been C) had been B) will have been D) had had
4. The effects of acid rain on aquatic ecosystems … investigated before the end of the century.
A) has not been C) had not been B) have not been D) will be
5. We … disconnected already before the talk was over.
A) have been C) will have been B) has been D) had been​