The basic fundamental feature(s) that enable us to broadly classify the animal kingdom is|are

The basic fundamental feature(s) that enable us to broadly classify the animal kingdom is/are
The basic fundamental feature(s) that enable us to broadly classify the animal kingdom is|are
The basic fundamental feature(s) that enable us to broadly classify the animal kingdom is|are
The basic fundamental feature(s) that enable us to broadly classify the animal kingdom is|are

is/are