Step 1: Identify redundancy. The phrase "cooperate together" is redundant since "cooperate" already implies "together."
Step 2: Analyze options.
- (a) Correct → concise and grammatically sound; avoids redundancy.
- (b) Wrong → repeats redundancy "cooperate together."
- (c) Wrong → awkward placement of "together"; still redundant.
- (d) Acceptable → "cooperate with each other" is correct, but option (a) is more concise and natural.
Step 3: Final sentence.
The best option is (a):
"If we cooperate by dividing up the booty, we shall be able to work together smoothly in the future."
\[
\boxed{\text{If we cooperate by dividing up the booty …}}
\]