What is a difference between a synchronous API and an asynchronous API?

What is a difference between a synchronous API and an asynchronous API?
A . An asynchronous API can make offline calls while synchronous APIs do not have this capability.
B . Synchronous API calls are returned immediately while asynchronous calls do not guarantee an immediate response.
C . Synchronous API calls require an authentication header to be sent while asynchronous calls do not require authentication.
D . An asynchronous API can make a larger number of calls in a specified time period than a synchronous AP

Answer: B

Explanation:

Reference: https://stackoverflow.com/questions/36213948/what-is-the-difference-between-asynchronous-calls-and-callbacks