Ah, the -ing contrast error as I call it!
The Iroquois were primarily planters, but supple-
menting their cultivation of maize, squash, and
beans with fishing and hunting.
(A) but supplementing
(B) and had supplemented
(C) and even though they supplemented
(D) although they supplemented
(E) but with supplementing
A - but supplementing - wrong. folks, the ing modifier canNOT appear with but. The obvious reason, the ing modifier clause builds up on the opening clause. It does NOT indicate a contrast. Check the meaning, the second clause is actually showing a contrats to the first one. Also, note here that ing is not a progressive tense. it is a modifier.
B - and had supplemented - wrong again. two reasons. 1. and cannot show a contrast. it is usually used to link two independent clauses. the intended meaning is a contrast. 2. had supplemented - incorrect tense. it indidcates that this action was before they were planters. incorrect meaning. the actions are simultaneous and the tenses should be consistent. both - simple past.
C - and even though they supplemented - incorrect. this indicates a contrast - meaning-wise correct. but this is not a complete sentence. it is a fragment. [i]]and[i] must connect independent clauses. the second clause does not have a working verb that will make it an independent clause. it is wordy too.
D - although they supplemented - wow! correct! although indicates contrast. they supplemented is correct. also, althouth needs a clause (sub + verb) this clause has both - correct. the tense supplemented (simple past) is correct as well. it is consistent with the non underlined tense.
E - but with supplementing - this is a modifier, not a verb. same error, ing modifier that is introducing a contrast. does not work. incorrect.
Take-aways -
Although needs a clause
Ing modifier cannot indicate a contrast