Answer:
c. the cost of teaching increased.
Step-by-step explanation:
If the marginal benefit of the corporta job decrease, then is less attractive to change job.
if the cost of corporate job increase, there is less gain thus, less attractive to move to this kind of job.
Last, if the benefit of teaching increased; with more reasons now, he professor will continue with their teaching activity.
From the given options: Only if the cost of teaching increase enought it may reconsider changing job.