Correct Option (B)
The original statement indicates that "some [supporters of ‘party X’, who knew Z and supported his campaign strategy] had friends in ‘party Y’." The existence of a friendship is a reciprocal relationship. If a supporter of Party X has a friend in Party Y, it logically follows that this friend, who is a supporter of Party Y, also knows the supporter of Party X. Therefore, it must be true that there is at least one supporter of Party Y who knew some supporters of Party X as a friend.
Incorrect Options:
(A) The provided information specifies the stance of certain supporters of Party X regarding the alliance. It offers no data or implication about the agreement or disagreement of any supporters of Party Y concerning the alliance. Thus, this statement cannot be definitively concluded as true.
(C) The initial premise explicitly refers to "supporters of ‘party X’, who knew Z and supported his campaign strategy." This phrasing directly implies the existence of supporters of Party X who did support Z’s campaign strategy. Therefore, this statement contradicts the given information and must be false.
(D) The premise states "supporters of ‘party X’, who knew Z". This indicates that there were indeed supporters of Party X who knew Z. Consequently, this statement is contrary to the given information and must be false.