Option 1 -> "Easy" means simple to understand, which is the opposite of abstruse.
Option 2 -> "Obscure" means unclear or difficult to understand, which is a synonym of abstruse, not an antonym.
Option 3 -> "Cryptic" means mysterious or difficult to interpret, which is similar in meaning to abstruse.
Option 4 -> "Mysterious" means difficult to understand or explain, which aligns with the meaning of abstruse.
Hence, Option 1: Easy -> "Abstruse" means difficult to comprehend or obscure, so its antonym would be something straightforward and simple to understand -> correct