Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight. this occurs because their cells are impaired in what way? a) they cannot replicate dna. b) they cannot undergo mitosis. c) they cannot exchange dna with other cells. d) they cannot repair thymine dimers. e) they do not recombine homologous chromosomes during meio

The correct answer is d) they cannot repair thymine dimers.
Thymine dimers (or pyrimidine dimers) are formed in DNA via photochemical reactions (exposure to UV light). Usually, those changes inside the DNA are recognized by DNA repair enzymes and fixed by photoreactivation (opposed mechanism of photochemical reaction). People with Xeroderma pigmentosum have a genetic disorder of that  DNA repair and thus, are unable to repair damage caused by UV light.