Restriction enzymes recognize and cut:
a.
random dna base-pair sequences
c.
single-stranded dna
b.
double-stranded dna
d.
rna

double -stranded DNA

Explanation:

A restriction enzyme is a DNA-cutting enzyme that recognizes specific sites in DNA. Many restriction enzymes make staggered cuts at or near their recognition sites, producing ends with a single-stranded overhang. If two DNA molecules have matching ends, they can be joined by the enzyme DNA ligase

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.