Sequence the following stages of the sliding window protocol for flow control.
A. Sender moves the window to the next set of frames.
B. Sender sends a window of frames.
C. Receiver acknowledges the received frames.
D. If acknowledgment is not received, sender retransmits the frame.
Choose the correct answer from the options given below:

1. AB, A, C, D
2. BB, C, D, A
3. CB, D, C, A
4. DB, C, A, D

Pick an option to check yourself, or open the answer below.