T hey all seem natural. Note that C and D have different meanings. In C, you didn't know his name then, but maybe you know it now.
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seagull. A man whose name I don't know came to me.For the intended meaning, D is the logical answer. If you used 'didn't', it then may suggest you know his name now.
Practical EnglishFor the intended meaning, D is the logical answer.Seagull didn't tell us which meaning was intended.