Answer:
Dolce
Step-by-step explanation:
The wonderful thing about Latin words in music is that it is easy to see the roots of each word. When the root is known, it is much easier to eliminate wrong answers. For example; agitato means agitated, 'ag' means anger, so this would obviously not be used in a lullaby score. Con Brio means 'with vigor', again, not good for a lullaby. Vivace means 'brisk and bright', while this could be an answer, dolce is the best answer. Dolce means 'soft and slow', much like a lullaby should sound.
Hope this helps! :)