Answer:
2.
Step-by-step explanation:
"We shall endeavor in spite of THIS to keep the United States of America neutral. In the event of this not succeeding, we make Mexico a proposal of alliance on the following basis: make war together, make peace together..."
- Arthur Zimmermann
The text before this states:
“We intend to begin on the first of February unrestricted submarine warfare,”
Therefore, 2. is the correct answer.