Which best describes what the map method accepts and emits? 

It accepts a single key-value pair as input and emits a single key and list of corresponding values as output. 

It accepts a single key-value pairs as input and can emit only one key-value pair as output. 

It accepts a list key-value pairs as input and can emit only one key-value pair as output.  

It accepts a single key-value pairs as input and can emit any number of key-value pair as output, including zero.