Sentence improvement (subject verb agreement): choose the best substitute for the underlined part in the sentence below. The chairman with the other members of the board are touring Europe these days.

Introduction / Context:
This question focuses on subject verb agreement when two noun phrases are joined by a prepositional phrase such as \"with\". In English grammar, only the true grammatical subject controls the form of the verb. Examinations frequently test whether you can identify the main subject when extra information is inserted between the subject and the verb.

Given Data / Assumptions:

• Original sentence: The chairman with the other members of the board are touring Europe these days.
• \"The chairman\" is the main subject of the sentence.
• \"With the other members of the board\" is an accompanying prepositional phrase, not a second subject joined by \"and\".
• Options: have been on touring, is touring, have toured, no improvement.

Concept / Approach:
When the structure is \"A with B\" or \"A along with B\", the verb usually agrees with A, the first noun phrase, because B is only additional information. \"Chairman\" is singular, so the verb should be singular as well. Therefore, the plural verb \"are\" is incorrect here. The correct singular present continuous form for a singular subject is \"is touring\".

Step-by-Step Solution:
Step 1: Identify the core subject: \"The chairman\". Step 2: Recognise that \"with the other members of the board\" is a prepositional phrase that describes who is accompanying him but does not change the grammatical number of the subject. Step 3: A singular subject requires a singular verb: \"is\" rather than \"are\" in the present continuous tense. Step 4: Form the correct verb phrase: \"is touring\". Step 5: Check the sentence with this correction: \"The chairman, with the other members of the board, is touring Europe these days.\" This sounds correct and natural.

Verification / Alternative check:
A useful test is to remove the extra phrase: \"with the other members of the board\". The skeleton sentence becomes \"The chairman are touring Europe\" which is clearly wrong. If you instead write \"The chairman is touring Europe\", it is correct. Adding the phrase back does not change this requirement. This confirms that the correct verb is singular.

Why Other Options Are Wrong:
Option \"have been on touring\": This is grammatically incorrect because we do not normally say \"on touring\". The present perfect continuous form would be \"have been touring\", but even then the subject number would be wrong if treated as plural. Option \"have toured\": This changes both the tense and aspect of the sentence, suggesting a completed action in the past rather than an ongoing tour \"these days\". Option \"no improvement\": Keeping \"are touring\" continues the error in subject verb agreement with the singular subject \"chairman\".

Common Pitfalls:
Many candidates are misled by the phrase immediately next to the verb. Because \"members of the board\" is plural and close to the verb, they choose a plural verb. Always look back to the true subject of the sentence, especially when phrases beginning with \"with\", \"along with\", \"as well as\", or \"together with\" are present.

Final Answer:
The correct form is: The chairman, with the other members of the board, is touring Europe these days. Thus, the correct option is is touring.