Which of the following statements about the MapReduce framework are correct?

Question $4$Select one or more:

a$.$

The MapReduce framework must be able to handle concurrent transactions, which are common in a distributed computing environment.

b$.$

In the MapReduce framework, developers need to handle load balancing by writing code in the map and reduce functions.

c$.$

A reduce worker can only start a reduce task after all map workers finish their map tasks.

d$.$

The key$/$value pairs generated by map workers are directly sent to reduce workers as input.

e$.$

A reduce worker may start a reduce task while some map workers are still running their map tasks.