As it is used in line 33, the word cumbrous most nearly means:
F. comfortable. G. untruthful. H. mistaken. J. burdensome.
The best answer is J. The context makes clear that the process is very precise, and that any mistake has the serious consequence of proving guilt. This would make the swearing anything but "comfortable," which rules out F. H makes no sense in context and G is illogical, for if the "swearing" is dishonest it cannot be "without a mistake" (line 34). Given that the procedure seems quite involved and exacting, J is the best answer.