Explanation:

To throw down the gauntlet:
To challenge someone to an argument, to declare or issue a challenge

Ex. The senator threw down the gauntlet on the abortion issue. 

Ex. Just as much as SP and BSP have thrown down the gauntlet in Gorakhpur and Phulpur, the BJP with its unmatched money and muscle power and the state machinery at its disposal will leave no stone unturned to hold on to these seats.

Option B is hence the correct answer.