Synergetic and collaborative are synonyms. They connote "working together".

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One must pay heed to the word WHILE-- one must anticipate that there is going to be a shift somewhere in the sentense which indeed took place after the ,.

the clue- SINGLE handedly got reversed - and hence the asnwers B and C

First word 'While' suggests contrast in two sentences. So, the opposite of 'single handedly' is the answer. B && C

Collaborative and synergistic

kudos

kudos

My process:
solitary -- we have an "although," meaning we want something that means the opposite of "on his own." This doesn't fit the bill.
collaborative -- this works. It contradicts "on his own."
synergetic -- this works. It contradicts "on his own."
exegetic -- no clue what this meant.
unilateral -- "one-sided," which could suggest he did things on his own. No.
collusive -- no clue what this meant.