a$.(5$ points$)$ What is the purpose of ARP, and where do we use it$?($Not to exceed $5$ lines$)$

b$.(5$ points$)$ Explain the difference between the "Time to Live" $($TTL$)$ field and the "Protocol" field in the IP header. $($Not to exceed $3$ lines$)$

c$.(5$ points$)$ Explain the two timers that ARP uses. $($Not to exceed $3$ lines$)$

d$.(5$ points$)$ Suppose machine D receives an ARP request sent from B looking for target C$,$ and suppose D has the binding for IP of host B to HWB in its ARP cache. Should D answer the request? Explain why or why not. $($Not to exceed $2$ lines$)$