In the Selective Repeat Automatic Repeat Request protocol if the receiver didn't receive frame $7$

but received frames $8$ and $9,$ what will the receiver do:

Question $6$Answer

a$.$

Send NAK $7$ immediately after receiving frame $8.$

b$.$

Send ACK $8$ and $9$ immediately after receiving frames $8$ and $9$

c$.$

Discard$/$drop frames $8$ and $9$ and wait for frame $7$

d$.$

Send NAK $7$ immediately after receiving frame $9$

e$.$

Send NAK $7$ immediately after receiving frames $8$ and $9$