BOTH Richard AND Elaine will babysit the twins on Saturday.
BOTH and AND are the conjunctions used to complete the sentence.
Conjunctions are words that serves as glue. Conjunctions join together words, phrases, or clauses.
There are three types of conjunctions:
1) Coordinating Conjunctions
2) Subordinating Conjunctions
3) Correlative Conjunctions
BOTH is a correlative conjunction.
AND is a coordinating conjunction.