A design engineer wants to construct a sample mean chart for the service life on a new lightbulb. Previous samples revealed that the service life was normally distributed with a mean of $500$ hours and a standard deviation of $20$ hours. On the recent production batches, service life on random samples of three headlights were:

$\backslash$table$[[$Sample$,$Service Life,,$],[1,495,501,503],[2,515,497,503],[3,488,495,499],[4,512,503,506]]$

What is the sample mean of the $2$ nd sample?

$500$

$499$

$505$

$508$