The top layer of soil in the tundra that thaws in the summer is called the
a. active zone
b. dense mat
c. photic zone
d. permafrost

A.

Explanation:

The arctic soil is so cold that the ground beneath the tundra surface remains frozen all year. This permanently frozen ground is called permafrost. Each summer, when the sun warms the tundra surface, the top few inches of soil thaw. This melted part is called the active layer.

i think the answer is 95 hope this

they had the law tat factories that produces smoke cannot be built near residential buildings.

building of proper sewage system was done to ensure that the waste is carried away from the humans so that they do not get diseases from it.

also they built water systems to provide water in those areas which are drought prone.