Answer:
Option C. is correct.
Explanation:
According to Chargaff's rules, DNA (Deoxyribonucleic Acid) from any species of an organism should have purine and pyrimidine bases in the ratio 
This ratio is very important for solving the structure of DNA.
As per this rule, DNA is double-stranded, and covalent bonds between identical nucleotides hold the strands together.
So, Option C. is correct.
The answer is A.
Thrift-store donations choices supports a circular economy.
A thrift store receives donated items or sells goods on consignment. It is run by a not-for-profit group instead of a merchant. The reason for establishing a thrift store is to raise money for charities through the not-for-profit group. The money realized in a thrift store is used to fund a non profit organization or other charity.
The correct answer is B. Possible side effects of a new medical treatment or product.
Explanation
A side effect is a concept that refers to the effect that a drug or treatment produces on the patient. Generally, when a drug is produced, a clinical trial is necessary to prove its effectiveness. This requires the participation of several volunteers who will test the drug and verify its effectiveness. However, these clinical trials have risks for volunteers since they can bring them negative effects because they are going to test drugs that have never been used before, so they must give their consent through a document called "informed consent. "where the volunteer is informed about the possible risks that the clinical study may have on him and if he is willing to undergo the test. Therefore, one of the main topics discussed during an informed consent is the possible side effects that the clinical study can bring to inform the volunteer of these conditions and confirm that he agrees with them. Therefore, the correct answer is B. Possible side effects of a new medical treatment or product
