Is My dog aggressive?

Asked: Is My dog aggressive?Today me and my dog went for walk. while we walk i saw my neighbor and there dog.Make note that this is the first time my dog (Pitbull) and his dog(Yorkie) meet.when my dog saw his dog he low crawled and keep walking.but my neighbor wanted to met y dog so my neighbor walk toward us my dog got scared his tail was under him and hair where standing up when i saw that told him to sit and relax.but after i said that he started growling like a nasty growl if that make

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