How does a client app communicate with Hyperledger fabric chaincode (Smart Contracts)?

How does a client app communicate with Hyperledger fabric chaincode (Smart Contracts)?
A . The app uses an SDK which invokes functionality on the chaincode which then announces the transaction to any peers required to endorse the transaction
B . The app uses Hyperledger Composer to communicate with CouchDB which in turn invokes chaincode functionality
C . Client apps don’t communicate with Hyperledger fabric directly, they must use Hyperledger Composer for the transmission
D . The app points to a node’s IP address, then calls an invoke function on the chaincode address to start the write process

Answer: A