Mix sieved flour, baking soda, salt, yoghurt and 1 tbsp of oil together. Use palm to knead. Add water gradually to make a soft yet not sticky dough. Apply some oil on the surface of the dough and cover it up with a cloth. Let the dough sit for about 3 hours in warm place. (把过筛的面粉,小苏打粉,盐,酸奶和1汤匙的油混合在一起。用手掌揉, 慢慢加入温水,揉到面团软而不粘。在面团的表面抹上一层油,然后用布盖着。让面团在温热的地方发酵约3小时。)