souvik101990 wrote:
Concerns for the environment have led chemists to develop plastics that are degradable. All degradable plastics, which are potentially useful packaging materials, need just the right conditions to break down. Some need exposure to sunlight, some need to be buried in soil, and some need to be submerged in water. It should be cautioned that some degradable plastics leave residues of unknown toxicity.
If all of the statements above are true, which one of the following must also be true?
The final sentence is the key sentence that most of the answer choices are referring to.souvik101990 wrote:
(A) Some materials that are potentially useful for packaging leave residues of unknown toxicity.
Absolutely. This is stated in sentence #2 and the final sentence.souvik101990 wrote:
(B) Some degradable plastics need both sunlight and submersion in order to break down.
Not necessarily. We know that some need sunlight, some need to be buried, some need to be under water. We don't necessarily know that some need two of these conditions in order to break down.souvik101990 wrote:
(C) Some materials that need sunlight in order to break down are not potentially useful packaging materials.
Out of scope. We know that all degradable plastics, which have potential to be useful packaging, need a certain action to occur in order for them to break down.souvik101990 wrote:
(D) Some materials that leave residues of unknown toxicity are not degradable plastics.
Out of scope. We are only talking about degradable plastics here. There may or may not be other materials that leave toxic residues. Who knows? We sure won't make any assumptions, especially in a must be true question!souvik101990 wrote:
(E) Some materials that need to be buried in soil to break down leave residues of unknown toxicity.
We only know that "some degradable plastics leave residues of unknown toxicity." And some of these degradable plastics require certain actions to be broken down. Yes, sunlight, burying in soil, and submerging in water are the 3 actions that we know that lead to certain plastics being broken down. But we don't know for sure that the ones require being buried in soil are the ones that leave toxic residues.