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’.

The branch of biology that studies the different structures and functions of the cell is called Cell Biology or Cytology.

 
Cell biology (formerly called Cytology), is a Greek word: kytos, "vessel" is a branch of biology that studies the different structures and functions of the cell and focuses mainly on the idea of the cell as the basic unit of life.

The cell (from Latin cella, meaning "small room") is the basic

• Structural,

• Functional (and) 

• Biological unit of all known living organisms. 

A cell is the smallest unit of life that can replicate independently, and cells are often called the "building blocks of life". 

The regional rural bank is not allowed to trade in over-night borrowing market.Scheduled commercial banks (excluding RRBs), co-operative banks (other than Land Development Banks) and Primary Dealers (PDs), are permitted to participate in call/notice money market both as borrowers and lenders.Overnight borrowing market, also known as call market, generally involves borrowing and lending of funds for one day and generally takes place against government securities.

Tatra not an Air Defence Missile System. It is a Czech manufacturer producing vehicles in Koprivnice. It is owned by the Tatra Trucks company, based in Ostrava, and is the third oldest company in the world producing cars with an unbroken history.