cheese
A hammer is useful when putting up a shelf. Studying is useful if you want to get a good grade on a test.
most of the product use in civil but most useful in civil 3d,revit,3dmax etc. . . .
The most useful object in the world is a screw. not kidding
Figures relating to a budget that are developed from the "bottom-up" following a participatory process are going to be the most useful.
Evaluating alternatives
Most useful and more useful.
more useful, the most useful
Yes, "useful" is a compound word made up of the root word "use" and the suffix "-ful" which means "full of."
It depends on how you use it. If it is just a "classic" one-liner, most girls will be quite annoyed and offended. If you can manage to put some effort in and come up with something original, then it might work.
more useful, most useful
It depends on what subject you're on.
Typically in American English the statement would be "a cow is a useful animal" - the first sound in useful is close enough to a consonant that most individuals will use "a" rather than "an".