其次，該研究未能引用其他更新的研究。

其次，該研究未能引用其他更新的研究。

Kết quả (Anh) 1:

Second, the study failed to cite other newer studies.

Kết quả (Anh) 2:

Second, the study failed to cite other updated studies.

Kết quả (Anh) 3:

Secondly, the study failed to cite other updated studies.