To answer this question, we need to know which country the Castro sibling is the president of.
Option A) Romania - This option is incorrect because the Castro sibling is not the president of Romania. The president of Romania is Klaus Iohannis.
Option B) Cuba - This option is correct. The Castro sibling, specifically Fidel Castro and later his brother Raul Castro, were presidents of Cuba. Fidel Castro served as the Prime Minister from 1959 to 1976 and then as the President from 1976 to 2008. Raul Castro succeeded his brother and served as the President from 2008 to 2018.
Option C) Venezuela - This option is incorrect. The current president of Venezuela is Nicolas Maduro.
Option D) Israel - This option is incorrect. The current president of Israel is Isaac Herzog.
The correct answer is B) Cuba. The Castro sibling, specifically Fidel Castro and later Raul Castro, were presidents of Cuba.