What makes one dna molecule different from another?
the number of strands that make it up

a. the sequence of bases along the strands

b. the type of sugar it has in each strand

c. the number of phosphate it has

Sequence of base along its strands

Explanation:

Deoxy ribonucleic acid (DNA) is a double-helical structure made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The nitrogenous bases found in DNA structure are four viz; adenine (A), thymine (T), guanine (G) and cytosine (C). These bases are the same in almost all individuals but the order or sequential arrangement of these nitrogenous bases is what determines the instructions given to a specific DNA or genetic code, which is actually the basis of difference between each DNA molecule.

"do a testcross with a homozygous recessive plant."