Happen is a synonym of Pass. Pass is a synonym of Continue. Continue is a synonym of Proceed. Do is a type of Proceed. 
Oral is related to Taste. Taste is related to Bad. Bad is the opposite of Adequate. Adequate is similar to Sufficient. 
Happen <--Synonym--> Pass <--Synonym--> Continue <--Synonym--> Proceed <--IsA-- Do 
Oral <--RelatedTo--> Taste <--RelatedTo--> Bad <--Antonym--> Adequate <--SimilarTo--> Sufficient 