A step implied but left out is to ignore the "No/None/Not both/Cannot/etc." indicator when negating and writing the statements.

I struggled with this section. One thing that helps to think about for which part is sufficient and which necessary is to give counterexamples that are the negation of each clause.

For example, on question 2: "Businesses do the environmentally “right” thing only if doing so makes good business sense." We have 2 clauses:

Do ... right thing ...

Makes good business sense ...

To give a negation example, let's ask "What if doing so makes only ok business sense? Can businesses do the environmentally right thing then?" No, it is explicitly stated that businesses do the right thing *only* when doing so makes "good" business sense. There is a restriction.

On the other hand, let's ask "If businesses do an environmentally 'neutral' thing (or a 'wrong' thing), does doing so have to mean that action does not make good business sense?" No, we're not restricted given the information we have. The action could be environmentally neutral and make a lot of good business sense.

So we know that the clause "Good business sense..." is the necessary part (which doesn't rely on the action being environmentally "right").

I got question 3 wrong, but reinterpreting the sentence as "Only written-down oral myths have survived" helps since the wording is deceptive.

Another way to look at the question is to imagine the set relationships. Written down myths are the superset, because surviving myths must be in that set (since there are no surviving myths that were not written).

By that principle, "written down" is necessary for the myth's "survive" which is exactly what the sentence is saying. i.e. "survived" is sufficient to say that the myth was "written down".

For this type of question, I was also confused about whether we were comparing species of corn together rather than Sorghum v. Other species. My understanding is to try thinking of another example: "Circles are more round than flat."

Step 1: What are we comparing? Circles v. flatness?

No, circles are merely the object we do the comparison on (Same role "Some cultivars of corn..." plays).

We compare roundness v. flatness, the way that sorghum is compared in proximity than "...most other cultivars...".

Step 2: What are we comparing? Whichever trait circles are more closely related to, same as proximity to "Some cultivars...".

I've found that the way the sentence is structured is confusing. Rephrasing it as "Sorghum is much more closely related to some cultivars of corn than to most other cultivars of corn." can help see a bit better.

Step 3: What is the winner? Roundness/Sorghum. Hopefully this helps you as well!

I got this question correct but it took me long to figure out. I think the habit of referring back to the referents in the clauses help to hammer home what information the author precisely brings up in a clearer way since it can remind you while you're reading.