a.$.$ What$$s the most significant difference between Router and Switch?

b.$.$ Which domain($($s)$)$ is/$/$are collision domains? ($($Note that smartphone, Laptop0$0$ and Laptop1$1$ are connected wirelessly and there$$s no VLANs configured)$)$

Domain a is _______________$\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_$ domain. ($($broadcast and/$/$or collision

Domain b is _______________$\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_$ domain. ($($broadcast and/$/$or collision)$)$