The correct answer is: C. Should
The word “should” is used to express a recommendation or suggestion. In this case, the speaker is recommending that the listener ask the speaker’s son to come home at once.
The word “will” is used to express a prediction or certainty. In this case, the speaker is not predicting or certain that the listener will meet the speaker’s son in the market.
The word “while” is used to express a time relationship. In this case, the speaker is not expressing a time relationship between the listener meeting the speaker’s son and the listener asking the speaker’s son to come home.
The word “would” is used to express a possibility or willingness. In this case, the speaker is not expressing a possibility or willingness that the listener will meet the speaker’s son in the market.