The majority party constitute the group within the Senate that has the most power over what legislation is put on the agenda and whether it is passed. Option B is correct.
Members of the majority party generally decide the most significant questions presented to Congress. In addiion to this, members of the majority party also primarily control what will be considered by their chambers on a daily basis.
In the Senate, whoever has the majority will likely get more bills passed because they will garner more votes.
The treaty of Versailles, which was signed after WWI, restricted Germany in many ways, they were forced to pay off debts and keep a very small military. This led to the anger of Germany and other Axis aligned countries.