In an isolated intestinal muscle perfusion system, to investigate whether the contractile effect of a drug on the intestinal muscle is mediated by H1 receptors, one should:
选项：

A:add the drug to be tested first and observe the contraction curve, then add chlorpheniramine and observe the effect;
B:first add chlorpheniramine, observe the contraction curve, then add the drug to be tested and observe the effect;
C:Add chlorpheniramine, observe the contraction curve, elute, then add the drug to be tested and observe the effect;
D:Add the drug to be tested, observe the contraction curve, elute, add chlorpheniramine, then add the drug to be tested and observe the effect