Answer: A

Reasoning: At steady state for a continuous IV infusion, Css = infusion rate ÷ clearance.  Css = 1.6 mg min⁻¹ ÷ 640 mL min⁻¹ = 0.0025 mg/mL, which rounds to 0.002 mg/mL. Half-life influences the time to reach steady state, not the value of Css itself [Burak, 1991, PMID 2049775].