Question

blood is thicker than water make interrogatuve​

Answer 1

Interrogative: Isn't blood thicker than water?

Answer 2

Hi !

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Blood is thicker than water. (Interrogative)

→ Isn't blood thicker than water ?

Note that ;

• Interrogative doesn't means starting the statement with 'How, why, what etc.,' In most of the cases (same as in this one) the statement can begin with 'Is/am/are,was/were,will/shall' depending upon the tense of the statement.
• Adding a 'question tag' is must.
• When a statement is positive then the question tag must be negative or vice versa.

e.g : Mairah is more studious than lara.

→ Isn't Mairah more studious than lara ?