Twelfth night explores uncertainty and inconstancy in love. which set of lines in these excerpts from act ii, scene iv, shows that duke orsino considers men to be more easily swayed by passion than women?

"no woman's heart / So big, to hold so much; they lack retention"

This shows that Orsino doesn't think that women are able to stay constant in love like men (especially himself) can. He says they "lack retention" which means they do not retain the same feelings for a long time like men do.

They lack retention
Alas their love may be called appetite
No motion of the liver but the palate

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