Any chance of you doing your homework by yourself?

答えはbです。でも、なぜそうなるかと言うと、 a、が makes 角 the subject and is incorrect because the person who's being told this is the subject. b、を makes 角 the object and is correct. c、に makes 角 the direction that you're going to and is incorrect because "角 corner" itself is not a direction. d、も means "too" and is incorrect, but you can say あの角も右にまがってください if the person turned right at another corner right before this.

B!