Which of the following led to the successful protection of Richmond from McClellan?

a - The superior number of Confederate forces

b - Geographic obstacles

c - Use of modern weaponry

d - The people stood against the attack.

The answer is B.

Here is proof from the section.

(the Confederates caught and attacked part of McClellan's force separated from the main army by the flooded Chickahominy River.)

Because of the flood, part of their group separated from the main group and a flood is a Geographic obstacle

The correct option is option A. The superior number of Confederate forces. On June 20, Lee launched a surprise attack against McClellan, and for seven days pushed the Union forces back. McClellan established a new base on the James River and still had a good position for an attack on Richmond.