We can grow more crops if we can make the best use of rain. (Simple)

Water is one of the most useful elements in nature. (Positive)

= Very few elements in nature are as useful as water. (one of the very few)

It is a very important asset. (Exclamatory)

= What an important asset it is! (Subject it > what)

We can not pass a single day without water. (Interrogative)

= Can we pass a single day without water? (Negative sentence-এর ক্ষেত্রে not উঠে গিয়ে interrogative)

lts main source is the rain that creates streams, lakes and rivers. (Compound)

= Its main source is the rain and rain creates streams, lakes and rivers.(that দ্বারা rain কে বোঝানোয় 2nd clause-এর subject হিসেবে rain আসবে)

We have rain during the monsoon. (Complex)

= When it is the monsoon, we have rain. (During থাকলে when হয়)

Heavy rainfall often causes flood. (Passive)

= Flood is often caused by heavy rainfall (causes is caused (present indefinite)}