Arrange the following events in chronological order andselect the correct answer from the codes given below:1.Rio Earth Summit2.Publication of Brundtland Commission Report3.Enforcement of Montreal Protocol4.Publication of 'The Limit to Growth' Report

1. A

   1, 4, 3, 2

   1, 4, 3, 2 puts Rio (1992) first, which is last among these four.

2. B

   4, 2, 3, 1

   4, 2, 3, 1 is the order: Limits to Growth 1972, Brundtland Report 1987, Montreal Protocol in force 1989 (signed 1987), Rio Earth Summit 1992. That is the official key.

3. C

   4, 3, 2, 1

   4, 3, 2, 1 would place Montreal before Brundtland. Our Common Future (March 1987) precedes the September 1987 Montreal signing and the 1989 entry into force.

4. D

   4, 1, 3, 2

   4, 1, 3, 2 puts Rio second, decades too early relative to Montreal and Brundtland.

Summary. Official key is (b) 4, 2, 3, 1. Club of Rome, then sustainable-development report, then ozone protocol enforcement, then UNCED at Rio. Honour the stored letter (b).