Some of the following sentences are gramatically incorrect and some are correct. Find out which part of a sentence has an error and mark the part . if there is no error mark the part of your answer.
She `("is")/a` one of those person `("whom")/b`I am sure always `("do their best")/c` even `("in the most trying circumstances")/d ` `("No error")/e `

Explanation

(b)use .who . for .whom.