What is future perfect tense? how are we supposed to use ot in the questions?

The Future Perfect Tense usage.

1. Events that will have happened by a certain moment in the future. The moment is set:

a) directly: We will have moved by the end of the year.

b) by another event, expressed in the Present Simple: The train will have left when we arrive at the station.

2. A hypothetic action which is to happen before a point in the future. You will probably have read that article before this letter arrives.

the unsaturated fatty acid is a fat consist of one or more double bond in the fatty acid chain. if it contains one double bond then called as monounsaturated fatty acid however if, it contains more than one bonds called as a polyunsaturated fatty acid. true fatty acids are called unsaturated fatty acids as it reduces the risk of high blood cholesterol and good for health.