Please check my answer to the following question thank you.

Question

The combining form referring to the anatomic structure through which food passes into the body is called what ?

A. rect/o
B. appendic/o
C. gastr/o
D. or/o

My answer is D. or/o

Answer 1

I agree.

You can use etymonline.com to find different words’ origins. Origins also are in dictionary entries for words.