<p dir="ltr" style="text-align: justify;"><span><span style="">This question is a complex sentence. The main clause is “______ remains one more training session to be conducted,” ended with an adverb clause “before workers are allowed to operate the new machine.”</span></span></p><p><span style="text-align: justify;">Let’s focus on the main clause. The main clause “_______ remains one more training session to be conducted,” could fit the pattern: S + V + SC. The subject is the blank itself, the verb is the linking verb “remains”, and the subject complement is “one more training session to be conducted.” By following this pattern, the blank should be filled with a noun to serve as the subject of this clause. </span><br></p><p><span style="text-align: justify;">Which of the four choices can be used as the subject of the main clause? </span></p><p><span style="text-align: justify;">(C) </span><span style="text-align: justify;">These - "These" </span><span style="text-align: justify;"> should be eliminated because the demonstrative pronoun “these” is plural, but the verb “remains” is singular, which fails to meet the subject-verb agreement. </span></p><p><span style="text-align: justify;">(B) </span><span style="text-align: justify;">This and </span><span style="text-align: justify;">(D)</span><span style="text-align: justify;"> It</span><span style="text-align: justify;"> - "This" and "It" should be eliminated, too, because these two pronouns should refer to something already mentioned in a context, which is not the case in this question. </span></p><p><span style="text-align: justify;">(A) There - "There' is the correct answer. The word “there” here is used as an indefinite subject. The singularity or plurality of the verb in the main clause depends on the noun after the linking verb “remains,” not “there.” Since the noun “one more training session” is singular and the whole question is used in the simple present tense, it’s correct to add “-s” after the verb “remain.” </span><span style="text-align: justify;"></span><br></p>