💡 Detailed Explanation
The correct choice is 'おいし' (stem form of 'おいしい'). The grammar pattern '〜そうだ' (looks like / seems) for expressing conjectural appearance or impression requires dropping the final 'い' of I-adjectives. Thus, 'おいしい' becomes 'おいしそう'. Sentence translation: 'This soup looks very delicious, doesn't it? It has a nice smell.' The other options ('おいしい', 'おいしくて', 'おいしさ') are incorrect grammatical connections for this pattern.