Question

what was mccormicks first major innovation that changed the way grain was harvested?
the mechanical reaper.
the practice of buying on credit.
the self - rope hand binder.
the twine binder.

Explanation:

Cyrus McCormick's mechanical reaper revolutionized grain - harvesting by automating the process, replacing manual scythe - based harvesting. Buying on credit is a business practice, not a harvesting innovation. The self - rope hand binder and twine binder are later developments related to binding harvested crops, not the first major innovation in harvesting.

Answer:

The mechanical reaper.