What is the first sentence of neck joint and parallel joint?

These two parts are the third sentence and the second sentence respectively.

Neck couplet is the third sentence of metrical poem, and parallel couplet is the second sentence. Every two sentences of a metrical poem are a couplet, the first couplet (1, 2 sentences) is called the first couplet (or couplet), the second couplet (3, 4 sentences) is called the parallel couplet, and the third couplet (first couplet).

Rhyme is a genre of China's traditional poetry, which belongs to the category of modern poetry. Named for its strict metrical requirements. Metric poems are generally eight sentences each, and more than eight sentences are called parallel sentences or long sentences.