How do carboxylic acids and esters differ in chemical structure?

Question

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Esters have a hydroxyl group.
Esters have a carboxyl group.
Esters have a carboxyl group and hydrogen linkage off the alpha carbon.
Esters have a carboxyl group and ether linkage off the alpha carbon.

Answer 1

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Esters are RCOOCR'
Acids are RCOOH

Answer 2

Esters have a carboxyl group and ether linkage off the alpha carbon