Question

the element known as the combining form
multiple choice
can never begin a word.
is the foundation of the word that provides its meaning.
can only appear once in a term.
is the combination of two roots and a combining vowel.
is the ending of some words.

Explanation:

A combining form is a root plus a combining vowel. It can be part of a larger word - formation process and is not restricted to starting, ending a word or appearing only once. The foundation of a word that provides its meaning is a root. A combining form is the combination of two roots and a combining vowel.

Answer:

is the combination of two roots and a combining vowel.