Bacteria Are Grown in a Medium Containing [¹⁵N]H₄Cl for a Number

Bacteria are grown in a medium containing [¹⁵N]H₄Cl for a number of generations so that all of the DNA is made of fully 'heavy' DNA. The bacteria are moved to a new medium and grown in [¹⁴N]H₄Cl so that all subsequent new DNA will be 'light.' If replication were dispersive, what would the DNA look like after two generation times?

A) All of the DNA is made of two 'light' strands.
B) Half of the DNA is made of two 'light' strands and half of the DNA is made of one 'light' strand and one 'heavy' strand.
C) All of the DNA is made of one 'heavy' strand and one 'light' strand.
D) Each strand is made of a mixture of 'heavy' and 'light' DNA, with each strand being between 75% and 100% 'light.'
E) Three quarters of the DNA is made of two 'light' strands and one quarter is made of two 'heavy' strands.