original_query: What defensive structures are being erected in the Sitzenabive Factory District?
query: What defensive structures were erected in the Sitzenabive Factory District during the defense of Serpukhov in 1941?
answer: During the defense of Serpukhov in 1941, anti-tank ditches, slabs, barricades, crevices, bomb shelters, and gas shelters were erected in the Sitzenabive Factory District.