vietmoi999 wrote:normally, "will do" is used for present time. But, in many gmat sc questions, and in the good material, "would do" is used for present time. I do not understand this point. I already read some grammar books but see no good explanation.

pls, help explain. which grammar book is good and contain this explanation?, pls share. Thank you

neither "will" nor "would" is used for present tense. They both talk about future.

So when some says, "will you do x" ? you reply saying that "will do". so you will do that thing in future; at current you are not doing x.

now you use would in the similar manner when you are talking about future from past's perspective.

for example - if i were you, i would study hard for my exam.

hope that helps.

"WILL" is used for future
"wouldd" is used for future in the past. "yesterday he said he would learn gmat"

but many cases, "would " is used for future , time of speaking is present. for example:

" I would learn gmat". the time of speaking is present.
above sentence happen frequently in gmat and on good material. pls,explain the use of "would" when the time of speaking is present.

'Will' is used to depict future tense or for predictions. 'Would' is used both as the past tense of 'will' and to depict hypothetical situations.
If current trends continue, carbon emissions in the United States will soar to ridiculously high levels by 2010.
Here, a prediction is being made - so 'will' is correct.

If the EPA had taken appropriate measures, carbon emissions would not have soared...
This is a hypothetical situation. So 'would' is correct.

There is always a confusion between the usage of "will", "would" and "would have". Here, remember these 3 conditional sentence forms as a thumb rule:

IF something happens THEN something else will happen
IF something happened THEN something else would happen
IF something had happened THEN something else would have happened [/list][/list]