What Are the Functional Groups in Alantolactone?

[τheory]

Homework Statement

Given the structure of Alantolactone, find two functional groups.

2. The attempt at a solution
This was a question that was on my exam recently. I answered Ester and Ether, however Ether was marked incorrect. Instead, only the answers Ester and Alkene were accepted.

How is Ether incorrect if R-O-R' found in the structure?

 

[Borek]

-O- is accompanied by carbonyl, so it is no longer an ether.

It is like calling a carboxylic acid an alcohol, just because carboxylic group contains -OH.