i. If we can extend the LAN then why we need a WAN?
ii. How can a bridge know whether to forward frames?
iii. Can the length of an Ethernet be increased to many segments of 500 meter each merely by adding a repeater to connect each additional segment?
iv. How can a computer attach to a network that sends and receives bits faster than the computer’s CPU can handle them?

1. LANS and WANS are separated into similar groups of devices operating for a common cause, policies and efficiencies. LANS are logical in that they are administered by classroom, building or even city. Even though these are known as MANS (Metropolitan Area Networks). WANS are connected to LANS in order to have a passage way for sharing data.
Analogous to this question would be - IF we can extend a city, why do we need a state? Hmmm?

2. Basically, a bridge is a device that sits between network segments and is self programs itself to distinguish packet routes. The bridge only hands over the packets to wherever they need to go either - local homogenous or disparate networks. Some bridges do NOT translate packets from one network to another however.

3. Interesting question, as this is how telephony circuit data are propogated. However for ISO/IEEE standards there is a limit. Don't know this limit.

4. Cache... simply cache.