Even today many people are guided by abstruse moral values.

Answer: Option B

Irrational : not logical or reasonable.
Obscure ; not clearly expressed or easily understood.
Impracticable : (of a course of action) impossible in practice to do or carry out.
Dangerous : able or likely to cause harm or injury.
Abstruse : difficult to understand; obscure.

Synonym of Abstruse is Obscure