Explanation

 The phrase “on duty” means اپنے فرض نبھانے میں مصروف

Explanation

We generally use about with concerned.

About is a preposition here.

Concerned about something means کسی کے بارے میں فکرمند ہونا

I am not concerned about his affairs.

Explanation

We generally use from with diseases.

From is a preposition here.  

She is suffering from a bad throat infection.

Explanation

The correct preposition is "in" when referring to something affecting a specific location or area.

So, "in our area" correctly describes where malaria has become a problem.

Explanation

His zeal for work is known to everybody.

Explanation

He is heir to his grandfather's prosperity.

وہ اپنے دادا کی خوشحالی کا وارث ہے۔

Explanation

There is a canteen beside book shop at school.

Beside means بغل میں یا قریب 

Explanation

You can maintain a healthy life, if you keep exercising.

Explanation

We use preposition by for means of transport. 

When we use "by" this way, it means "close to" "next to" or "beside."

Explanation

The preposition "of" is commonly used to describe the content or amount associated with something, such as "a cup of tea" or "a cheque of fifty thousand rupees."