Questions

Mesopotamian Civilization (4000 BC - 6th Cen. BC)

Egyptain Civilization (3400 BC - 1000 BC)

Harappan Civilization (2500 BC - 1750 BC)

Chinese Civilization (1765 BC - 250 BC)

An electric charge always flows from a body at higher potential to a body at a lower potential irrespective of the amounts of charges contained in them. In the question , no current flows. So there is no potential difference. 

The sentence is grammatically and contextually correct. ‘His’ is the correct form of pronoun to be used. Thus, the correct formation would be, ‘He reached his destination at night’.

If some action has started in the past and is still continuing, then present perfect continuous tense should be used instead of present continuous tense. So, the phrase ‘am waiting’ needs to be replaced with ‘have been waiting’ to make the sentence contextually correct. Thus, the correct formation would be, ‘I have been waiting for three –quarters of an hour’.