Step 1: Understand the core argument.
The passage argues that low physical fidelity simulations are acceptable because the main requirement is that naturalistic decision making of soldiers in stressful, simulated combat situations should not be compromised.
Thus, the central claim is: \emph{as long as decision-making ability is preserved, low physical fidelity simulation is valid}.
Step 2: Identify weakening statements.
To weaken this claim, we need statements that show decision-making \emph{is compromised} or that simulations \emph{cause uniform, artificial behaviour rather than true individual decision making}.
- (i) High physical stress weakens decision-making capabilities → directly weakens the assumption that naturalistic decision making remains intact.
- (ii) High mental stress affects adaptability → though true, this does not directly negate the passage since it focuses on physical vs. cognitive fidelity distinction. Less relevant.
- (iii) Simulated environments as good substitutes → this strengthens, not weakens.
- (iv) Simulated exercises cause systematic “common” behaviour → this reduces naturalistic, individual decision making, thus weakens.
- (v) Officers prefer battle-hardened soldiers over simulation-trained → while interesting, this is about selection practices, not directly about decision-making ability in simulations.
Step 3: Correct combination.
The statements that best weaken the argument are:
- (i) Weakening of decision-making by stress.
- (iv) Uniform behaviour undermines individuality in decision-making.
\[
\boxed{\text{Answer: C (i and iv)}}
\]