Argument Analysis: the majority party has unity in the senate much more than in the lower house (the House)
(A) On 30 key issues, 18 of the 67 majority party members in the Senate voted against the party leaders.
Correct -> this shows that the majority of the majority party members in the Senate have unity. (strengthens)
(B) On 30 key issues, 70 of the 305 majority party members in the House voted against the party leaders.
Shows unity in the lower house, however says nothing about the senate or upper house
(C) On 30 key issues, over half the members of the minority party in both houses voted with the majority party against the leaders of the minority party.
Does not give any basis of comparison
(D) Of 30 key legislative proposals introduced by the president, only eight passed both houses.
If same number is shown in both houses then the authors argument cannot be strengthened as is is based on comparison.
(E) Of 30 key legislative proposals introduced by a president whose party controlled a majority in both houses, only four passed both houses.
Same explanation as (d)