To answer this question correctly, the user needs to have knowledge of South Korean business etiquette. In South Korea, business cards are an important part of networking and exchanging contact information. Therefore, it is essential to treat them with respect.

Now, let's go through each option and explain why it is right or wrong:

A. Write on it: This option is incorrect. You should not write on a South Korean's business card as it is seen as disrespectful. In South Korea, business cards are viewed as an extension of the person and should be treated with respect.

B. Comment on it: This option is incorrect. You should not comment on a South Korean's business card as it may be considered impolite. Instead, it is recommended to receive the business card with both hands, examine it briefly, and then put it away in a cardholder or a safe place.

C. Look at it: This option is correct. You should definitely look at a South Korean's business card when it is presented to you. It is considered rude not to look at the card when it is offered to you.

D. Comment & Look at it: This option is incorrect. As mentioned earlier, you should not comment on a South Korean's business card, but it is essential to look at it carefully and receive it with respect.

Therefore, the answer is: A. Write on it