In What Way(s) Can Ethereum Smart Contract Functions Be Invoked

Multiple Choice

In what way(s) can Ethereum Smart Contract functions be invoked?

A) Only through code executed in other Smart Contracts and XML-RPC
B) Through code executed in other Smart Contracts and through web3.js or any JSON-RPC library
C) Only through code executed in another Smart Contract
D) Smart Contracts cannot be externally invoked. They become autonomous at launch and cannot be called.