Xiao Ming likes to guess a riddle with his friends.

小明喜欢和朋友们一起猜谜。

Mother would accumulate the river sand into a large heap drying in the open and then riddle with a screen before selling to the building boss.

母亲需要把捞上来的河沙堆积成一个巨大的沙丘，在空气中晾晒干后，用筛子再筛一次，然后才能卖给建筑商。