Months after last taking a drug, a former drug abuser still produces very little serotonin. The person is depressed and anxious and has great difficulty remembering new material. MOST likely, the abused substance was:

LSD / Ecstasy

Explanation:

A deregulation in the production of serotonin can generate several mood disorders, mainly anxiety and depression.

This can be related to the constant use of drugs such as LSD or Ecstasy. These drugs act directly on the serotonin receptors, causing uncontrolled stimulation, leading to dependence.

By removing the constant consumption of the drug (and consequently the high stimulation), possibly through specific treatments, it will take time for the body to get used to it again and produce serotonin at normal levels.

Esctasy

Explanation:

Ecstasy  generally is the street name for 3-4-methylenedioxy -methamphetamine(MDMA).

it  usually increases sensations, and perceptions of color and sounds.This class of drug usually contain hallucinogenic substances and therefore have profound effects on the minds, Creating imagination of unrealistic scenes, state of euphoria,increasing  energy.

They do this by increase the level s of release of serotonin. Therefore, after withdrawing  the elevated levels of serotonin still presented withdrawal symptoms as evident in the question.

Cocaine, heroin,caffeine etc belongs to this class of drugs. sometimes called the love pills. They usually bring bad memories of the past,uncontrollably,  to have negative effect on the present  and therefore create rooms for  depression, anxiety, state of paranoid and deep confusion, thus they sometimes said to create illness of minds

the backbone of the dna and rna compound is sugar phosphate.

the correct option is option d