He always vocalizes his thoughts actively when the teacher asks questions.

vocalizes 是动词 vocalize 的第三人称单数现在时形式。vocalize 由词根 vocal（声音的、发声的）加上动词后缀 -ize 构成，意思是"用声音表达"或"发声"。在这里指"表达出自己的想法"。