Ich mochte ...... Kaffee trinken
A
Correct answer
Explanation
In German, 'einen' is the correct article here. 'Ich mochte einen Kaffee trinken' means 'I would like to drink a coffee'. Since 'Kaffee' is a masculine noun and is the direct object of 'trinken', it takes the accusative case, which is 'einen'. 'Einem' is dative, 'eine' is feminine nominative/accusative, and 'ein' is masculine nominative or neuter nominative/accusative.