Answer:
B. foster
Step-by-step explanation:
Definitions-
Promote: further the progress of (something, especially a cause, venture, or aim); support or actively encourage.
Foster: encourage or promote the development of (something, typically something regarded as good).
If you look at these definitions you can see that both "promote" and "foster" encourage a process or development. They also both support something and are normally regarded as good. Therefore you can see that they are very similar in meaning, you just might prefer one or the other depending on the sentence you use it in. Finally, this also shows that these two words are great synonyms of one another!
I hope this was helpful! :)