No, exams can not be interchange with examination. exams is the plural form of examination.

could is used to show abilities in the past or to show humanity regarding ability but should is used to show morality and discipline it is also past form of shall.

it depands on situation. for examples:- Water is very useful to live. the water is dirty. when we use articles before common noun, its meaning changed. water:- water to drink the water :- place where water is stored like ponds, river, well, handpump

yes this problem is also happened to me

we have in different situations as follow when we show possession when we talking about the action that is done recently and "had been" is used in past perfect continuous tense as well as in the voice of past perfect tense

there is a great distance between must and should must is used to show necessity but should is used to show morality

light-festival

Gaya went to Gaya.

instead of 5000 rupees, you received 17-18 credits worth 5000 rupees.ok

if you want to improve your English skills then your first step should be thanking deeper and deeper. thinking is only way to learn English the best