Which part functions like a straw in the honeybee's anatomy?

The proboscis is the correct answer as it functions like a straw in the honeybee's anatomy. This elongated mouthpart allows bees to suck up liquids, particularly nectar from flowers. The structure of the proboscis is essential for feeding, and it has a flexible, tubular form that facilitates the uptake of liquids, much like a straw.

The glossa, while part of the proboscis, is specifically a structure that helps in the manipulation and collection of nectar. The labrum is another mouthpart that serves primarily as a protective cover for the mandibles and does not play a role in the sucking mechanism. The cardo is a segment of the insect's jaw that aids in moving the mouthparts but does not directly function like a straw.

Therefore, the proboscis is uniquely adapted for the important task of feeding, making it the key structure that performs this straw-like function in honeybees.