Though now eaten in large quantities around the world and harmless, the tomato is a member of the generally toxic nightshade family, including belladonna, and was once thought to be poisonous itself as a result.
A) Though now eaten in large quantities around the world and harmless, the tomato is a member of the generally toxic nightshade family, including belladonna, and was once thought to be poisonous itself as a result.

B) The tomato, though now eaten in large quantities around the world and harmless, is a member of the generally toxic nightshade family, which includes belladonna, and it was therefore once thought to be poisonous itself.

C) Once thought to be poisonous itself, the tomato is harmless and now eaten in large quantities around the world, and is a member of the generally toxic nightshade family, including belladonna.

D) Though now eaten in large quantities around the world and known to be harmless, the tomato was once considered poisonous because it is a member of the generally toxic nightshade family, which includes belladonna.

E) A member of the generally toxic nightshade family, including belladonna, the tomato was once considered poisonous even though it is harmless and now eaten in large quantities around the world.

Moreover, "including belladonna" is incorrect left dangling. It should be "which includes belladonna." -quoted form Mgmat. why?

Using the new method, the research was finished by the young professor.
I think the sentence is incorrect because of incorrect left dangling.

Also, refer to og 12, sc N0. 12, I think it uses including as E did. (since we are not allowed to post og question here. sorry.)

Could you help me understand this?

Thanks

I don't have an OG 12 handy to check that example you mention, but I'll try to address usage of "including."

The following would be correct:
Several edible plants, including the tomato and XXX, are members of the generally toxic nightshade family.

Many students, including members of my study group, were not able to complete the project due to emergency library closure.

Five local families, including the mayor's family, were displaced due to the flood.

In all cases, "including" follows (and modifies) a plural noun:
Several things, including something(s), do something.

In the CAT example you cite, "including" modifies either the generally toxic nightshade family or possibly a member. Either way, it doesn't make sense for a singular thing to be "including" anything.

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Emily Sledge
Instructor
ManhattanGMAT