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:

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

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

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

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

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

Clear my choice