The correct answer is A) preventing Azerbaijan from building a pipeline.
Russia has prohibited Azerbaijan from selling its oil by preventing Azerbaijan from building a pipeline.
Azerbaijan has plenty of oil deposits in its territory that is located in the western shore of the Caspian Sea. The government wants to invest more in the extraction and export of oil but Russia is its competitor and had prevented them to build a pipeline that crosses its territory. Russia doesn't want a pipeline that connects Azerbaijan to the Mediterranean Sea or the Black Sea. Russia wants Azerbaijan to still use the existing pipeline.