HW in networking , IP !!

Hi guys ,

I have a homework in networking consist from three Questions.

Q1: How many IP addresses can be associated with a host name and the other way around? Give an example.

for example ,, yahoo.com may has to ip address one is 192.168.1.1 and second 199.188.1.1 or three .. 

and also may be the ip address 192.168.1.1 has several host name for example yahoo , google or what ever . these are an example from my mind they are not true just for explain the Q1.

Q2: A hostname has an extension for example “.com, .net, .org, .edu”. What is this extension? Is it related to the IP address? 

Q3: How websites are blocked? And how its contents are identified? 

for example in my country the goverment block the websites that have a vidoes or photos about SEX . How they know the websites .. Are they visit it or is there an algorithims to find these sites and blocked automatically.

I with the Questions are clear ....