Which part of the following sentence contains an error ?

Both Raghunath as well as Ravish
(a)
have given
(b) their consent
(c)
to the new proposal
(d)

The correct answer is (a).

Explanation:

In English grammar, conjunctions are used in pairs (correlative conjunctions) or individually according to specific rules of usage.

The conjunction "Both" is always followed by "and", not "as well as". Using "as well as" alongside "Both" creates a redundant and grammatically incorrect structure.

Incorrect usage: "Both Raghunath as well as Ravish..."

Correct usage: "Both Raghunath and Ravish..." (or simply "Raghunath as well as Ravish...")

Therefore, part (a) contains the grammatical error.