Hint: Rec A is a type of protein that binds to a special type of DNA molecule which is not normal on the basis of the number of strands of the nucleotides in the DNA.
Rec A protein binds to Single-stranded DNA. RecA protein is weighted 38 kilodalton which is essential for the repair and maintenance of DNA. RecA's association with DNA major is predicated on its central role in homologous recombination. The RecA protein binds strongly and in long clusters to single-stranded DNA to make a nucleoprotein filament. The protein has over one DNA binding site and thus can hold a single strand and double strand together. This feature makes it possible to catalyze a DNA synapsis reaction between a DNA helix and a complementary region of single-stranded DNA.
Additional Information: RecA has multiple activities, all associated with DNA repair. within the bacterial SOS response, it's a co-protease function within the autocatalytic cleavage of the LexA repressor and therefore the λ repressor. The RecA protein catalyzes unidirectional branch migration and by doing so makes it possible to finish recombination, producing a part of heteroduplex DNA that's thousands of base pairs long. Since it's a DNA-dependent ATPase, RecA contains a further site for binding and hydrolyzing ATP. RecA associates more tightly with DNA when it's ATP bound than when it's ADP bound.
So, the correct answer is ‘Single-stranded DNA’.
Note: At the University of North Carolina the scientists Wigle and Singleton have shown that small molecules interfering with RecA function within the cell could also be useful within the creation of the latest antibiotic drugs. The inhibitors of RecA might be needed to enhance the toxicity of antibiotics.