Only 1,000 to 2,000 species of fruit flies exist worldwide. Nowhere in the world are fruit flies more taxonomically d...

Ross-Rinehart on February 7, 2022

This passage adds a bunch of fluff to a pretty basic argument structure. (This is common on Must Be True questions.) For many Must Be True questions, we can anticipate the correct answer if we first look for conditional statements. The last sentence here gives us a conditional statement:

Fruit Fly in Hawaii ? Descendant of One or Two Ancestral Females

Next, we can see if we’re given anything that applies to that conditional statement. The penultimate sentence says that the picture-winged drosophilids is in Hawaii. So, we can make the following conclusion:

Fruit Fly in Hawaii ? Descendant of One or Two Ancestral Females
Picture-winged drosophilids: Fruit Fly in Hawaii
Conclusion: Picture-winged drosophilids: Descendant of One or Two Ancestral Females

In other words, the picture-winged drosophilds must have descended from the same one or two ancestral fruit flies, since it’s a fruit fly in Hawaii and all fruit flies in Hawaii share that trait. This is why (A) is the correct answer.

(C) is not supported because we don’t know that all the fruit flies in the world come from the same one or two ancestral females. That was only true of fruit flies in Hawaii.