He died___ heart attack.

(a)by (b)from (c)of.

Please tell me correct option and also tell me why other two options are not suitable.

He died of heart attack

The preposition by is used to indicate the latest time at which an action will be over.
for example
The programme will be over by 9 p.m.

The preposition from indicates the starting point of an action. It is generally used with to or till/until
for example
The exhibition will be held from 15 February to 25 February, 2014
 

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(c)of

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(c)of

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(c)of

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