Bob would like to increase his earnings. the option most likely to increase his earnings potential in the long-term is to
a) spend money to renew current training.
b) take a similar position with a different company.
c) spend money for additional training and education.
d) laterally transfer to a different job within his company.

I think the correct answer is C)spend money for additional training and education. This is the only way to actually move up the ladder. Renewing his current training is unlikely to get him a substantially bigger salary. A similar position within a different company means that he would get more or less the same compensation. A lateral transfer wouldn't bring him more money either. The only way to increase his earnings, in the long run, is to acquire new skills while improving the ones he already has.