CO₂ has a lot to do with the so-called greenhouse effect. ✬

Plants require CO2 to grow. ✬

Tom co-wrote these songs. ✬

I talked to Tom's neighbors and co-workers. ✬

Both the pilot and the co-pilot are dead. ✬

Tom has co-authored three textbooks. ✬

Tom and Mary will co-host the show. ✬

I went over the itinerary with my co-workers. ✬

Tom called a co-worker for help. ✬

Tom has co-written three books. ✬