Which of the following is true about dna?
a. both of the original dna strands act as templates during replication.
b. it is a single-stranded molecule.
c. only one of the original dna strands acts as a template during replication.
d. its replication takes place in the cytosol

The correct answer is a. 

Option b is incorrect because DNA is composed of double-stranded molecules. 
Option c is incorrect because both strands of the DNA act as a template during replication (thus making a correct).
Option d is incorrect because replication takes place in the nucleus of eukaryotic cells.

It is called the medulla oblongata or people usually call it medulla. it is the lower half of the brain stem continuous with the spinal cord.