The authors' use of the words "exact," "specific,” and
"complement” in lines 47-49 in the final paragraph
functions mainly to
A) confirm that the nucleotide sequences are known
for most molecules of DNA.
B) counter the claim that the sequences of bases
along a chain can occur in any order.
C) support the claim that the phosphate-sugar
backbone of the authors' model is completely
regular.
D) emphasize how one chain of DNA may serve as a
template to be copied during DNA replication.

The correct answer is: D: emphasize how one chain of DNA may serve as a  template to be copied during DNA replication.

Explanation:

If the actual order of the bases  on one of the pair of chains were given, one could  write down the exact order of the bases on the other  one, because of the specific pairing. Thus one chain  is, as it were, the complement of the other, and it is  this feature which suggests how the deoxyribonucleic  acid molecule might duplicate itself.

In this excerpt, the authors use the words like "exact", "specific", and "complement" to explain how one chain of DNA may serve a base which will be copied during DNA replication. They use the mentioned words to explain the certain process, by trying to be specific and accurate and make the lecturers understand this process.

Plastic clogs their intestines and leads to slow starvation. Others become entangled in plastic bags and drown. Because plastic bags take hundreds of years to break down, every year our seas become 'home' to more and more bags that find their way there through our sewers and waterways.

Explanation: