In a polar, covalent bond, why might one area of a molecule be more negative then others of the molecule

Polar covalent molecules exist whenever there is an asymmetry, or uneven distribution of electrons in a molecule. One or more of these asymmetric atoms pulls electrons more strongly than the otheratoms. For example, the polar compound methyl alcohol has a negative pole made of carbon and hydrogen and a positive ...

It depends on the subject for me. some exams are easier than others so i usually go through it and answer questions i know based on my general knowledge, then double check after. going through the lesson can a lot  because the exams can be  very lesson-specific, but sometimes they are ridiculously long so a lot of people don't take the time. i did find that, when i went through the lessons, i was making 100's on my exams vs strictly using + the internet and  i make 90's.