The stimulus tells us about the qualities of degradable plastics—some qualities that all degradable plastics have, and some qualities that only certain degradable plastics have. All degradable plastics are potentially useful packaging materials, and they all need specific conditions to break down. To break down, some degradable plastics must be exposed to sunlight, some must be buried in soil and some must be submerged in water. Finally, some degradable plastics leave residues of unknown toxicity.

One way to think about all these claims is as conditional statements:
(1) degradable plastic → potentially useful for packaging
(2) degradable plastic → specific conditions to break down
(3) degradable plastic ←some→ _{break down}exposed to sunlight
(4) degradable plastic ←some→ _{break down}buried in soil
(5) degradable plastic ←some→ _{break down}submerged in water
(6) degradable plastic ←some→ unknown-toxicity residues

Another approach we can take is set logic: considering degradable plastics as a superset with certain qualities (potentially useful for packaging, needs specific conditions) that contains different subsets with their own qualities (breaks down in sunlight/soil/water, leaves residues).

Using either approach, we can start to think about interactions between these statements/sets that will allow us to make inferences. Specifically, any quality of the superset also belongs to the subsets: if all degradable plastics are potentially useful, that means degradable plastics which break down in sunlight are potentially useful, and so on. We can also state this as a set of new "some" statements: "some materials that are potentially useful for packaging break down in sunlight," and so on. Any statement of this kind, which is a logically valid inference, could be a correct answer.

In the answer choices, keep an eye out for invalid inferences that might try to trick us. For example, "nothing that is not a degradable plastic is potentially useful for packaging" and so on. If necessary, diagramming difficult answer choices is always an option, and can be useful to check against the claims in the stimulus.