Select the letter of the choice that identifies the function of the word

or phrase in quotes in the following sentence:
Minerals in the hollow part of a geode "can include" quartz, gypsum, or
even amethyst.
a. simple subject
b. simple predicate
c. complete subject
d. complete predicate

d. complete predicate

The function of the word or phrase "can include" in the sentence is the b. simple predicate.