What is a valid DataWeave expression to set as the message attribute of the Logger to access the value "Max" from the Mule event?

Refer to the exhibits.

The Set Variable transformer is set with value #[ [ first "Max" last "Mule"} ].

What is a valid DataWeave expression to set as the message attribute of the Logger to access the value "Max" from the Mule event?
A . vars "customer first"
B. "customer first"
C. customer first
D. vars "customer" "first"

Answer: D