Fill in the blanks with an appropriate verb form:

They…………………….. us for a long time.

have known

The correct answer is OPTION 1 - HAVE KNOWN

The complete sentence is: "They have known us for a long time."

This present perfect tense indicates that the action of knowing started in the past and continues to the present.

• "are knowing" is incorrect because "know" is a stative verb that is not typically used in the continuous form.
• "knew" is simple past and does not indicate the ongoing nature of the action.
• "known" is the past participle form and cannot stand alone without a helping verb.