Task: Question Answering
Input (English): Question: Esters can be obtained from carboxylic acids and alcohols, by applying the Fischer esterification reaction in which: 
 Options:  <1> A base is used as a catalyst. <2> A ketone is used as the solvent. <3> A reducing reagent is used. <4> An oxidizing agent is used. <5> Acid catalysis is used.
Output (English): 5