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