Medicines are often administered in pill form. in many cases, the active ingredient of the pill (the drug) is joined to another substance by this forms a/an which is stable in the dry environment of a pill bottle but dissociates under the wet conditions of the digestive system to release the drug to the body.

a. covalent bonds; salt
b. ionic bonds; salt
c. ionic bonds; acid
d. hydrogen bonds; base

Option B, ionic bonds; salt

Explanation:

All medicines either in the form of pills or liquid interact with our body by forming a bond with target specific receptors. For instance if a pain killer is taken then it shall form bond with receptors produced by pain and inflammation

So medicines are basically chemical which interact with biomolecules such as enzymes, nucleic acid, hormones, ions etc. by forming ionic bond, hydrogen bond, van der wall force etc. in the active site of enzyme.    

These salt molecule remain stable in normal conditions but as they come in contact with digestive system of the body (with different pH) they release the drugs

Hence, option B is correct

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).