*Form 3CD is a questionnaire with 32 questions. the tax auditors has to provide his comments on those 32 questions.
Form 3 CA or Form 3 CB is the report (Covering letter) which needs to be followed by Form 3 CD & its annexures.
The report should be in Form 3 CA if the entity is liable to audit under any other statue and already that statutory audit for the same period is completed before tax audit & you have relied upon those audited accounts to provide tax audit details.
If the entity is not liable to any other statutory audit or no such audit is completed prior to tax audit then Form 3 CB needs to be used.