The English physician Edward Jenner found that if experimental subject

Himanshuv0

Yeah, that OG explanation is not very good. The team that writes the explanations is clearly not on the same level as the team that produces the questions.

Since B and D have other flaws, it’s not necessary that the -ing modifier be incorrect. “Fake” splits are common in SC! The -ing modifier makes a fair amount of sense here, but it does create a slight difference in meaning. The noun modifier in A/C/E tells us that cowpox causes a mild infection in general. So the idea is that we can infect someone with cowpox (not so bad) to prevent smallpox (a worse disease). Since B/D uses an adverbial modifier, these sentences are saying that the act of infecting someone deliberately with cowpox causes only a mild infection. This leaves open whether this is true of all cases of cowpox, or only those resulting from deliberate infection. That’s not a huge flaw in B/D, but I believe that’s what the OG explanation is trying to address.