• Choice A is the present tense form of the verb used for "now" or "everyday". (I know your name.)
• Choice B is the passive form of the verb. (He was known by the police.=The police knew him.)
• Choice D is the present perfect plural tense used for something in the past that continues in the present. (They have known her for years.=They still know her now.)
The correct answer is C.The simple past tense is needed