He, busy-appearing, is. [Syntax]

The correct answer is "忙(いそが)し" (isogashi). This sentence uses the pattern "Adjective-そう/Verb-そう" (seems Adjective/Verb). For i-adjectives like "忙(いそが)しい" (busy), the final "い" is dropped before adding "そう" to form "忙(いそが)しそう" (seems busy). Therefore, "彼(かれ)は忙(いそが)しそうです" correctly means "He seems busy". "彼(かれ)" is the pronoun for "he", and "は" is the topic particle, both already present. "そうです" is the auxiliary verb for "it seems" and comes after the adjective stem.

正解は「忙し」です。「V/Adj-そう」は「〜そうだ」という様態を表す表現です。い形容詞に接続する場合、最後の「い」を取り除いて「そう」をつけます。「忙しい」は「忙しそう」となります。したがって、「彼は忙しそうです」が正しいです。「彼」と「は」はすでに文中にあり、「そうです」は形容詞の語幹の後ろにくるため不適当です。