💡 Detailed Explanation
The suffix '〜そう' (sou) translates to 'looks like...', 'seems...', or 'about to...'. It expresses the speaker's immediate, intuitive judgment of a state or a highly likely near-future event based purely on visual observation. It attaches to the 'ます' stem of verbs or the stem of adjectives. It represents visual inference, so it cannot be used for known facts. In this sentence, it translates perfectly as: "That cake looks very delicious.". The correct option 'そう' dynamically matches the structural requirements and logical flow of the statement. The other options do not satisfy the grammatical construction or fail to convey the appropriate semantic nuance.