Drawing two altitudes of a triangle

I am trying to construct a triangle with 2 altitudes. It worked for ‘All’ vertices.

a = {5, 0}; b = {0, 0}; c = {3, 6}; tri = {a, b, c}; alt = TriangleConstruct[tri, {"Altitude", All}]; Graphics[{Style[Triangle[tri], Opacity[0.2]], alt}] 

But when I tried to specify two vertices,

alt = TriangleConstruct[tri, {"Altitude", {a, b}}]

The following message came out:

TriangleConstruct is not a Graphics primitive or directive.

How do I specify two vertices to draw the altitudes?