这是他的胳膊用英语是 "This is his arm."
来源：这是一句基本的英语句子，由主语"this"，谓语动词"is"，定语"his"和名词"arm"组成。
例句：
"This is his arm, it's broken." (这是他的胳膊，断了。)
"Can you move your arm? This is your arm." (你能动动你的胳膊吗？这是你的胳膊。)
"Look at the size of his arm muscles! This is his arm." (看看他胳膊肌肉的大小！这是他的胳膊。)