An international group of more than 2000 scientists project an average global warming that will be between be between 1.8 and 6.3 deg farenheit by the year 2000.

1...........

2. project an average global warming to be from 1.8 to

3. project global warming that will be between 1.8 and

4. projects global warming to average from 1.8 to
5. projects an average global warming of between 1.8 and

Why is E preferred over D?

stupid question (that doesn't affect the grammar of the sentence in any way): are you sure the year in the question is supposed to be 2000?

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choice e is better than choice d because choice d exhibits poor idiomatic usage, in two ways:
- the group projects global warming to average - nope, can't do this. i've seen the infinitive when 'project' is used in the passive voice (as in 'statistic x is projected to increase to ...'), but only then.
- an average is not a range of numbers, so it's incorrect to say average from X to Y. you can average between x and y - meaning that the average will be one value, somewhere between those two - but not from x to y.