By

Subordinating conjunction

  observing

Verb

  these

Determiner

  subjects

Noun

,  Johnson

Proper noun

  helped

Verb

  Masters

Proper noun

  identify

Verb

  the

Determiner

  four

Numeral

  stages

Noun

  of

Adposition

  sexual

👉👌

Adjective

  response

Noun

.

By observing these subjects, Johnson helped Masters identify the four stages of sexual response.

By observing these subjects, Johnson helped Masters identify the four stages of sexual response.