This cake is sweet and delicious. [Syntax]

The correct answer is "あまく" (amaku). This is the て-form stem of the い-adjective "あまい" (amai, sweet). It's used to connect adjectives, describing multiple qualities of the same noun. Here, it connects "sweet" and "delicious." "ケーキ" (keeki) is the noun meaning "cake." "は" (wa) is the topic-marking particle, which comes after the noun. "て" (te) is the particle that connects the て-form stem to the next part of the sentence; it should come after "あまく."

正解は「あまく」です。い形容詞「あまい」のて形語幹で、複数の形容詞をつなぐときに使われます。「ケーキ」は名詞、「は」は助詞で、名詞の後に来ます。「て」は接続助詞で、「あまく」の後に続きます。