The dutch elm pathogen is spread from an infected elm tree to a healthy tree by1.wind-blown or rain-splashed spores2.root grafts3.both wind-blown/rain-splashed spores and infested elm bark beetles4.both infested elm bark beetles and root grafts5.infested elm bark beetles

5. infested elm bark beetles

Explanation:

Research publication (TERRY A. TATTAR, in Diseases of Shade Trees (Revised Edition), 1989) provided the detail on Dutch elm disease. According to researcher it is caused by Ceratocystis ulmi (fungus). Elm bark beetles carry this fungus from infected wood to the healthy wood.

well the answer is 2!

actually the answer is c