The Iroquois were primarily planters, although they supplemented their cultivation of maize, squash, and beans with ?shing and hunting。 翻译过来:易洛魁人以种植者为主,虽然他们也通过打渔和打猎来补充其玉米、南瓜和豆的种植。
being primarily a planter is not closely related to how they plant their crops (u r being reminded of this point as the original choice use the contrast word “but”)
alternatively,being primarily a planter is closely related to a sentence saying that they plant a wide range of crops
also,the existence of primarily gives u a great signal that the latter clause should not share the equal importance that the former has
you should read the sentence more carefully to really grasp the core meaning