Qual è la differenza tra It was natural that he harbor resentment toward her. e It was natural that he harbors resentment toward her. ?Sentiti libero di rispondere con un esempio.

@Tomo97
So this gets tricky. Right off the bat, your first sentence doesn’t sound right to my ears.
I had to look this up to give you a decent explanation, and it’s still difficult:

In English, the -s is only added to regular verbs in the present tense when the subject of the verb is a third person singular subject. This -s is different from the plural -s. Do not confuse the two.

The subject "Lisa and Ronald" is a third person plural subject, so the verb does not get an -s.

Below is a chart showing the regular verb drop with different subjects, both singular and plural.
drop singular ↓ plural ↓
first person →I drop the ball. We drop the ball.
second person →You drop the ball. You (all) drop the ball.
third person →He/She/It drops the ball They drop the ball.

To boil this down, he is third person so it would be harbors and not harbor.

I hope this helps and is not too confusing