In this sentence completion question about tense and subject verb agreement, choose the option that best completes the sentence: "As the festival approaches, the number of customers _________."

Introduction / Context:
This question tests your understanding of correct tense and subject verb agreement in a sentence that describes what usually happens when a festival approaches. The focus is the phrase "the number of customers" and its correct verb form in a general truth context. Many learners are confused by the presence of the plural noun "customers" and pick the wrong verb form.

Given Data / Assumptions:

• Sentence: "As the festival approaches, the number of customers _________."
• The clause "As the festival approaches" is in simple present and states a regular situation.
• Subject of the blank: "the number of customers".
• Options: Will have increased, Has increasing, Will be increased, Increases.
• The sentence describes a general pattern, not a one time future event.

Concept / Approach:
First, identify the true grammatical subject. The phrase "the number of customers" is singular because "number" is the head noun. For general truths and regular patterns, English usually uses the simple present tense. Therefore, we need a simple present verb that agrees with a singular subject. The form "increases" is the simple present singular form of "increase" and fits perfectly. The other options either use future forms or incorrect combinations that do not match the grammar or meaning.

Step-by-Step Solution:
Step 1: Recognise that the clause "As the festival approaches" indicates a general or repeated situation, so the main clause should also be in simple present. Step 2: Identify the subject of the main clause: "the number of customers". Even though "customers" is plural, the head noun "number" is singular. Step 3: Choose the simple present singular verb "increases" to agree with "the number". Step 4: Insert it into the sentence: "As the festival approaches, the number of customers increases." Step 5: Confirm that the sentence now describes a general, habitual trend in correct tense and agreement.

Verification / Alternative check:
Consider each incorrect option. "Will have increased" is future perfect and introduces unnecessary complexity, suggesting a completed action by a specific future time, which is not the intended general statement. "Has increasing" is grammatically wrong, as "has" must be followed by a past participle, not "increasing". "Will be increased" puts the verb in passive voice, as if someone actively causes the number of customers to increase, which does not fit this natural trend description. None of these choices fit as well as "increases".

Why Other Options Are Wrong:
"Will have increased" is a future perfect tense that is unsuitable for stating a simple, regular pattern.

"Has increasing" is incorrect because after "has", we require a past participle like "increased", not a present participle like "increasing".

"Will be increased" uses a passive construction, more appropriate for things like "rates will be increased", not for the natural growth in customer numbers.

Common Pitfalls:
Students often get distracted by the plural noun "customers" and forget that the real subject is "the number". A good rule is: when a sentence has "the number of + plural noun", the verb is singular. When it has "a number of + plural noun", the verb is usually plural. Remember also that general truths and habitual actions are normally expressed with simple present, not complicated future or perfect tenses.

Final Answer:
The correct completion is "increases", so the sentence should read: "As the festival approaches, the number of customers increases."