Pyongyang, metroovagun № 231

Pyongyang,  Changchun DK4  № 097 
Pyongyang — Chŏllima Line (천리마선) — Yŏnggwang Station (영광)

Станция метро Ёнгван [Yŏnggwang Station] 영광

This image shows a 4 axle trailer car, most likely built by Kim Jong Tae locomotive works, which is different from the DK4 as it has no air conditioning, and has no cab on either side. The side fluting also appears higher.
These cars were most likely built to expand the DK4 from a 2 car set into 3 and 4 car sets.

source: https://gamp.ameblo.jp/venus1969/entry-12427078884.html

1990-e a
Saatis jiachen