Hi ugimba,
Thank you for your question. Let's start by looking at the most obvious difference between each answer: project vs. projects.
The subject of the sentence is "An international group," which is a
singular subject that needs a
singular verb to match. The verb "project" is a plural verb, so we should rule out any answers that use "project": A, B, & C.
Now we're left with answers D & E. While they look similar, they mean different things:
(D) projects global warming to average from 1.8 to
This means that
the temperature of the Earth will be somewhere between 1.8 and 6.3 degrees Fahrenheit by the year 2000. If this is true, we're not talking about global warming - it's going to be cold! The way this is written changes the meaning, so it is incorrect.
(E) projects an average global warming of between 1.8 and
This is the correct answer because it uses proper subject-verb agreement, and it keeps the intended meaning. This answer says that Earth will warm between 1.8 and 6.3 degrees MORE than what it already is, which is what the writer intended to say.
In the end, we're left with the correct answer: E.