Your sentences is correct (aside from word spacing) although it may not be the best one for the given meaning. 1. 오빠는 많은 문장이 *word*으로 시작하는 것 같아요 = 오빠는(topic) [많은 문장이 *word*으로 시작하는 것 같아요]. = With you [in your case], a lot of of sentences seem to start with *word*. 2. 오빠는 많은 문장을 *word*으로 시작하는 것 같아요. = You seem to start a lot of sentences with *word*. (2) is clear and simple with a matching structure to the English sentence. (1) is a two-tiered sentence uniquely Korean, similar to 나는 병원에 가는 것이 싫다. It first sets the high level topic (오빠는), and then states the detail with a subject(많은 문장이) and predicate (... 같야요). In everyday speech, we would say it more colloquially like these: - 오빠는 무슨 말도[말이든] 다 *word*으로 시작하는 것 같아요 = You seem to start every sentence with *word*. - 오빠가 하는 말은 (뭐든지) 다 *word*으로 시작하는 것 같아요 = Every sentence you say seems to start with *word* (no matter what).