Questions

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’.

Mixed heart means the heart in which the oxygenated and the deoxygenated blood is mixed. Reptiles and amphibians have mixed heart.

Tea bag is what it will go in dry and come out wet, the longer it is in, the stronger the tea we will get.

Numismatist: someone who studies or collects coins, paper money, or medals.

Philatelist: a person who collects stamps.

Ornithologist: a person who studies on birds.

Statistician: an expert in the preparation and analysis of statistics.