Concept:The dialogue reveals that drug and alcohol abuse is a social vice and a form of moral corruption that hinders national development.
Explanation:Wanja plans to take marijuana and alcoholic drinks at a night club just to get high and be seen with fear and respect.
Ada warns that people who abuse drugs often face psychiatric problems or premature death.
Ada advises Wanja to build a good character and avoid becoming the cause of his own downfall.
This shows that bad habits like substance abuse corrupt the lives of youths and reduce their contribution to society.
Corrupt practices of any kind slow down progress, lower productivity, and prevent national development.
Option A (low poverty level) and Option D (multi-party system) are not barriers but signs of progress.
Option B (rural-urban migration) is not supported by the dialogue.
Therefore, the major barrier to national development shown here is the prevalence of corrupt practices.
Answer:C. prevalence of corrupt practices.