“Hall sensed that [it] would tip the balance in favor of the U.S. joining the Allied forces”
This states the same as the question prompt. In this evidence it shows that there is an assumption that it, the telegram, will result in the "U.S. joining the Allied forces." In the first option it only shows that people waited to show Wilson the telegram, not that it would make an impact on the decision to declare war. The second option doesn't work because it speaks of the policy provoking the U.S., but does not give any indication that the British were waiting or had any interest in what the U.S. would do. The last option simply states that the U.S. declared war. It doesn't show any hesitation or evidence of the telegram.