The correct answer is (B). marchers were attacked by police as they crossed a bridge.
The Selma march was led by John Lewis and other activists aiming to cross the Edmund Pettus Bridge over the Alabama River en route to Montgomery. But just short of the bridge, they found their way blocked by the local police who ordered them to turn around and go back. When the protesters refused, the officers shot tear gas and waded into the crowd, beating the nonviolent protesters with billy clubs.
The correct answer is b. marchers were attacked by police as they crossed a bridge.
When the marchers reached the Edmund Pettus Bridge they were attacked by the state and local lawmen who used billy clubs and tear gas to drive the protesters back to Selma.