TASK DEFINITION: In this task, you are given two sentences in the English language (Sentence 1 and Sentence 2). Your task is to identify the connecting word between the two sentences.
PROBLEM: Sentence 1:The second pre-production train was also tested on the Victoria line during engineering hours , and was expected to begin trial running in full passenger service in July 2008 . Sentence 2:However , this date slipped twice , first to January 2009 and then to July 2009 .

SOLUTION: however

PROBLEM: Sentence 1:Pastrana resigned and returned to Colombia and Samper rejected his own appointment . Sentence 2:But this move was not well received by the Conservative Party .

SOLUTION: but

PROBLEM: Sentence 1:Plasmids , the circular DNAs shown in Fig. 1 , are generally used for non-viral gene delivery . Sentence 2:However , there are two major problems with most methods for delivering DNA to cellular chromosomes using plasmids , the most common form of non-viral gene delivery .

SOLUTION:
however