Analysis: According to the meaning of the question, the geometry is a triangular prism, so the radius of the largest sphere is the radius r of the inscribed circle of the right triangle in the side view.

Solution: According to the meaning of the question, the geometry is a triangular prism, so the radius of the largest ball is the radius r of the inscribed circle of the right triangle in the side view.

Then 10? r+ 10？ r= 10

√2

Centimeter,

∴r= 10？ five

√2

≈3 cm.

So choose: a.