Most people experience multiple choice tests to be more easy than open questions. Psychologically this can be explained by memory processes of generating and recognizing .
Open questions initiate a searching process for generating different possible answers first.
In a second step the correct answer is recognized and selected. For multiple choice only the second step is necessary, the recognizing. When beginning a new lesson, you shouldn't overtax yourself with generating translations. After you perfectly learned the lesson you'll gain nothing by boring yourself with recognizing. Take your time to examine the vocabulary items, try categorizing and delimiting them.