The correct options are
B ΔAMN is a right angled triangle.
D AM is an altitude.
Since AM is perpendicular to side BC and passes through a vertex A, it acts as an altitude. An altitude may or may not pass through the midpoint.
Since, ∠AMC = 90∘, ΔAMN is a right angled triangle.
In case of an equilateral triangle, altitude passes through the midpoint of the opposite side. So, it acts as both altitude and median.