Where are the grana located?
a. in the stroma
b. in the thylakoids
c. in the inner membrane
d. in the intermembrane space

The best answer is "a" - in the stroma.

In the chloroplast are two membranes, and inside  the inner membrane is the gelatinous matrix known as the stroma. the stroma contains DNA and ribosomes. Membranous sacs thylakoids are found arranged in stacks called grana, therefore grana are simply stacks of thylakoids.

Within the chloroplast, grana resemble stacks of green discs or pancakes and are not necessarily uniform in their height or distribution. 

 The shape of thylakoids stacked in grana allows for optimum surface area.

during the process of dna replication, brdu can replace thymidine and incorporate into the newly synthesized dna, cell proliferation thus can be reflected in the extent of brdu incorporation.

maybe because its impossible for balloons to lift a whole entire house.