Stimulus says that some organisms came about through endosymbiosis (one organism engulfing another). Then goes on to say that there's an unusual nucleomorph in plant C. What makes it unusual? Two versions of a gene in it. Then goes on to say that

/remains of engulfed organism nucleus -> find a single gene

/find a single gene -> remains of engulfed organism nucleus

In Plant C, we found two versions of a gene. So, it follows

/find a single gene-> remains of engulfed organism nucleus.

This means that endosymbiosis happened. Hence, E. Plant C has two genes because one organism engulfed another.

I hope this is helpful for those who had a harder time with this question!

@legallyhaya This is how I thought about this question:

The astronomer starts off by mentioning that these earlier estimates of distances of stars from Earth are known to be untrue. This is because this would mean that the stars are older than the universe, which couldn't possibly happen.

The astronomer then goes on to say that they have their own estimates; it is implied that they believe their estimates to be true. The astronomer's estimates are saying that the stars are farther away than what those earlier estimates (which are untrue) said.

So, the astronomer is saying the stars are (1) farther away and (2) not as old/younger than what was previously thought. This, thinking back on the first premise, also tells us that a closer star is older than a star that is farther away.

The next premise then says "the farther away the stars are, the greater their intrinsic brightness..." So, the stars are (1) farther away, (2) not as old/younger than what was previously thought, and (3) brighter.

From this, the astronomer's argument concludes that these new estimates help to explain the earlier conflict between the age of star and age of universe. Because if it's true that the star is farther away than what was believed, it is younger and brighter. Which helps to discredit that stars are older than the universe.

@Arthurxx If you're between a more strongly worded answer choice and a weakly worded one, go with the latter