This question tests your understanding of verb forms and passive voice in English grammar. The sentence "This form is _____ in ink" requires a verb phrase that correctly completes the structure.

The key grammatical concept here is the passive voice. The passive voice is used when the focus is on the action or the object receiving the action, not on who is performing the action. The structure is:

Subject + form of "to be" + past participle

In our sentence:

• The subject is "This form".
• The form of "to be" is already provided: "is".
• We need to complete the structure with the appropriate past participle form.

Let's analyze the options:

Step 1: Evaluate "has been filled"
This uses the present perfect tense ("has been"), but our sentence already provides "is". Using "has been" would create a grammatical error: "This form is has been filled" is incorrect.

Step 2: Evaluate "to have be filled"
This is grammatically incorrect. "Be" is not the correct form to use after "to have"; it should be "to have been filled". Even then, an infinitive phrase doesn't fit after "is" in this context.

Step 3: Evaluate "to be filled"
This is the passive infinitive. The structure "is + to be + past participle" is used to indicate that something must be done or is required to be done. This fits perfectly: "This form is to be filled in ink" means the form must be completed using ink.

Step 4: Evaluate "to fill"
This is the active infinitive. If we used this, the sentence would mean the form itself is performing the action of filling, which is illogical. A form cannot fill something; it is filled by someone.

Final Answer: The most appropriate word is "to be filled". The correct sentence is: "This form is to be filled in ink."

Related Concepts & Formulae

Passive Voice Formula:
Subject + [be verb] + past participle + (by + agent)

Passive Infinitive Formula:
[be verb] + to be + past participle

Key Theory: The passive voice shifts the focus from the doer of the action to the receiver of the action. It is often used in formal instructions, rules, and descriptions of processes, which is exactly the case in this sentence about how a form should be completed.