Parts of the following sentence have been given as options. Select the option that
contains an error.
The boy whose the sister is ill has left.

Correct option is D

The error is in "whose the sister." The correct phrase should be "whose sister" without the definite article "the." "Whose" already implies possession, so adding "the" is redundant and incorrect. The correct sentence should be: "The boy whose sister is ill has left."