The correct answer is - A) Permafrost used to be permanent.
The permafrost used to be permanent until recently, so using certain techniques of building on it functioned properly. But with the climate changes that are becoming more and more evident, the permafrost is no longer permanent, but instead, it is either defrosting in some part of year and then forming again, or has been totally absent from some regions in the present.
That has caused changes in the rules governing building on permafrost. The reason for the changes is that the old techniques do not work properly anymore, and the permafrost changes are making change in the landscape, making big damages on the infrastructure in meantime.
Answer:
Subsidence is so slow that there seems to have been no depression of the upper surface of the lithosphere, so depositional environments are mostly the
same as those in surrounding areas; the succession is just thicker. These
successions are also more complete, however—there are fewer and smaller
diastems—so at times the basin must have remained under water while surrounding areas were emergent. (A diastem is a brief interruption in
sedimentation, with little or no erosion before sedimentation resumes.)
Size, shape: rounded, equidimensional, hundreds of kilometers across
Sediment fill: shallow-water cratonal sediments (carbonates, shales, sandstones),
thicker and more complete than in adjacent areas of the craton but still
relatively thin, hundreds of meters.
Hopefully that helps!
