They sat together, studying carefully the blueprint of the building.这里为什么是studying,而不是and studied?即：They sat together, and studied carefully the blueprint of the building

They sat together, studying carefully the blueprint of the building.这里为什么是studying,而不是and studied?即：They sat together, and studied carefully the blueprint of the building
They sat together, studying carefully the blueprint of the building.
这里为什么是studying,而不是and studied?即：They sat together, and studied carefully the blueprint of the building

They sat together, studying carefully the blueprint of the building.这里为什么是studying,而不是and studied?即：They sat together, and studied carefully the blueprint of the building
因为前面已经有一个动词sat,再用一个动词时候要＋ing形式,如果用and studied要把逗号去掉才对,不然后一句就没有主语了