Task: Question Generation
Input (English): By 16:50, with the Prussian southern attacks in danger of breaking up, the Prussian 3rd Guards Infantry Brigade of the Second Army opened an attack against the French positions at St. Privat which were commanded by General Canrobert. At 17:15, the Prussian 4th Guards Infantry Brigade joined the advance followed at 17:45 by the Prussian 1st Guards Infantry Brigade. All of the Prussian Guard attacks were pinned down by lethal French gunfire from the rifle pits and trenches. At 18:15 the Prussian 2nd Guards Infantry Brigade, the last of the 1st Guards Infantry Division, was committed to the attack on St. Privat while Steinmetz committed the last of the reserves of the First Army across the Mance Ravine. By 18:30, a considerable portion of the VII and VIII Corps disengaged from the fighting and withdrew towards the Prussian positions at Rezonville.
Output (English): What factor immobilised the Prussian Guard?