If

Subordinating conjunction

  the

Determiner

  second

2nd

Adjective

  couple

👫

Noun

  declined

Verb

,  the

Determiner

  third

3rd

Adjective

  couple

👫

Noun

  was

Auxiliary

  asked

Verb

.

If the second couple declined, the third couple was asked.

If the second couple declined, the third couple was asked.