A patient receives a drug X, 100 mg , intravenously. The concentration of the drug in the blood measured at 1 and 8 hours after the dose are 9 mg / L and 3 mg / L respectively. If the decrease in the concentration of the drug follows

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1. Afirst-order kinetics, the rate constant is 0.156 ~h ⁻¹ .
2. Bfirst-order kinetics, and the next dose of the drug is to be administered when [ X ]=1 mg / L , then the next
3. Czeroth-order kinetics, and if the next dose of the drug is to be administered when [X]=1 mg / L and after 12 h
4. Dfirst-order kinetics, the half-life of the drug is 4 hours.