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Verse example 1: C F G7 C (I, IV, V7, I) --- Chorus ?

Verse example 2: C F Am G7 C (I, IV, vi, V7, I) --- Chorus ?

Verse example 3: C Am G C (I, vi, V, I ) --- Chorus ?

Here's what struck me, sitting in the office trying to imagine those chords:

Example 1: Go to D minor (or E minor)

Example 2: Go to G

Example 3: Go to D then to G