Comprehension: In the following passage, some of the words have been left out. Read the passage carefully and select the correct answer for the given blank out of the four alternatives.
The scene will now shift to obtaining __________________ instruments of ratification to bring the agreement into force _________________ 2020, the first year of its________________ implementation. The agreement will enter into force with the ratification of ______________ 55 countries, whose aggregate greenhouse gas (GHG) emissions ________________ at least 55 per cent of global emissions.

whose aggregate greenhouse gas (GHG) emissions ______ at least 55 per cent of global emissions.

1. A
   established
2. B
   constitute
3. C
   enact
4. D
   complement