The options are missing from the question,below are the options to choose from;
A) incorrect (or missing) routes in a routers routing table
B) incorrect DNS configuration on the PC
C) incorrect default gateway configuration on the PC
D) duplicate IP addresses on your LAN
Answer: The correct answer to the question is option A
INCORRECT (OR MISSING) ROUTES IN A ROUTERS ROUTING TABLE.
Explanation: When it is possible for a PC to ping some devices but not actually all,we can then make an assumption that either it has a wrong subnet that is configured or the router from the path to the remote device actually has an incorrect or a missing routes to the device.