What sentence structure error is present in 'is Ms. Ellis and Ms. Stephenson'?

In the phrase 'is Ms. Ellis and Ms. Stephenson', the error lies in the use of 'is' instead of 'are'. This phrase refers to two subjects, Ms. Ellis and Ms. Stephenson, which is a plural subject. In English, when a compound subject is joined by 'and', it requires a plural verb to agree with the multiple subjects. Therefore, the correct verb form to use in this case would be 'are', making the phrase 'are Ms. Ellis and Ms. Stephenson'. This ensures that the sentence adheres to the rules of subject-verb agreement, which are essential for clear and correct communication.