I watched a very interesting movie with a friend yesterday. [Syntax]

The correct answer is "えいが" (eiga). This is the noun meaning "movie," and it is the direct object of the verb "みました" (mimashita, watched). It requires the direct object particle "を" (o) after it. "とても" (totemo) is an adverb meaning "very," which modifies the adjective "おもしろい" (omoshiroi, interesting). "おもしろい" is an adjective that modifies "えいが." "を" (o) is the direct object particle itself, which should follow the noun.

正解は「えいが」です。「えいが」は動詞「みました」の直接の目的語となる名詞で、その後に助詞の「を」が来ます。「とても」は「おもしろい」を修飾する副詞です。「おもしろい」は「えいが」を修飾する形容詞です。「を」は目的語を示す助詞で名詞の後ろに来ます。