b
\(DIBAL-H\) acts as a reducing agent and it can reduce carbocylic acid group and its derivative into aldehyde group. Also, it can convert nitriles into aldehydes. So, both the groups, \(\left(- COOCH _{3}\right)\) and \((- CN )\) will get convert into \((- CHO )\) group. Therefore, option \(( B )\) is the correct.
