The answer is B. All of these are likely.
A particular species of beetle feeds primarily on purple colored roots. In a situation where a disease takes out a large population of the plant that produces the purple roots, the likely scenario would be that,
1. An amount of the beetles who eat purple colored roots will die. If the beetles fail at finding an alternative root for food source, they might die of hunger.
2. The beetles who adapt to eat red rooted plants will survive and reproduce. Some of the beetles who look for alternative root color can survive and not die of hunger, and become reproductive.
3. The beetles will find a new food source. The beetles on not finding purple colored roots will search for alternative food sources like dead roots and roots of various other plants, irrespective of whether they have color or not.