What would cause this changed behavior?

You add a GRE tunnel to transport packets between two routers. After implementing this, you
notice an increase in the number of dropped packets. While looking at packet captures, you notice
that the do-not-fragment (DF) bit is set in the IP header of all the dropped packets.
What would cause this changed behavior?

A.
The GRE tunnel has a lower MTU than the physical interface.

B.
GRE tunnels do not support fragmentation.