@7SageTutor thanks for this explanation. I fell for the “Thus” indicator. Your explanation helped me to understand the MC better. If we compress all of the “example” sentences down into a single sentence, it becomes easier to see that the MC is the overall conclusion, while the last sentence is just a sub-conclusion:

“It is well known that many species adapt to their environment, but it is usually assumed that only the most highly evolved species alter their environment in ways that aid their own survival. However, this characteristic is actually quite common. Certain species of plankton, for example, generate a gas that is converted in the atmosphere into particles of sulfate. {…and Thus,} plankton cause the surface of the Earth to be cooler and this benefits the plankton.”

@Jbshallenberger - I am also confused on #3. I went back to the previous video that introduced the Group 2 indicators, and "only" is at the top of the Group 2 indicators:

It helped me to understand #5 by adding the [bracketed] words below:

At least 59 percent of households maintained a lower indoor temperature [this year] than they had been accustomed to maintain on very cold days [last year].

"things" being compared: indoor temperature [this year] vs. indoor temperature [last year]

"quality" being compared: which temp was lower? 

"winner": indoor temp [this year]