Step 1: Understanding "Complaint".
As per Consumer Protection Act, a complaint can be filed for unfair trade practices, defective goods, deficiency in service, or overcharging.
Step 2: Analyzing options.
- (A) Correct, unfair/restrictive trade practices qualify as complaints.
- (B) Correct, defective goods are also a ground.
- (C) Correct, charging excess price is also a valid complaint.
Step 3: Conclusion.
Since all are correct, the answer is (D).