$4\mathrm{.}2-5.$ Packet dropping. Suppose a datagram is switched through the switching fabric and arrives to its appropriate output to find that there are no free buffers. In this case:

Select one:

a$.$ The packet will be dropped $($lost$).$

b$.$ The packet will be sent back to the input port.

c$.$ The packet will either be dropped or another packet will be removed $($lost$)$ from the buffer to make room for this packet, depending on policy. But the packet will definitely not be be sent back to the input port.

d$.$ Another packet will be removed $($lost$)$ from the buffer to make room for this packet.