The backbones of dna and rna are

a. identical.
b. very different, made of nucleotides in dna and amino acids in rna.
c. made of alternating sugars and phosphate groups.
d. made of a chain of base pairs.

The answer is very likely C.

Explanation:

This becomes easy once we remember that DNA and RNA are not identical - which is why they have different names, RNA = 'ribo', DNA = 'deoxy.' This eliminates choice (A).  While they are different, they are not incredibly different - DNA and RNA are both made up of nucleotides - they are not however, made up of Amino acids. Amino acids are what they can code for, and subsequently create proteins during protein synthesis. This helps us eliminate (B). Finally, we know that in order for something to have base pairs it needs to be double stranded - which RNA is not. Which means that because RNA is not double stranded (its singly stranded) that the answer cannot be (D). Leaving us with the only plausible option; (C).

the answer is; comparing the frequency of collisions with and without the device

this makes the anti-collision system an independent variable and the collisions a dependent variable. if there are fewer collisions with an anti-collision system that without, then it can be stated that the system is a success. essentially, collisions under an anti-collision system are compared with the frequency of collisions by cars with the human drivers.

the truman doctrine was an american foreign policy whose stated purpose was to counter soviet geopolitical expansion during the cold war. it was announced to congress by president harry s. truman on march 12, 1947, and further developed on july 12, 1948, when he pledged to contain threats to greece and turkey.