Which of the following statements about permafrost is true?

(a) it is rare in periglacial environments.
(b) permafrost that thaws and refreezes produces a pentagonal or hexagonal ground surface pattern called columnar joints.
(c) it can extend as deep as 1,500 km below ground surface.
(d) it can melt to a depth of a few meters in summer, then refreeze in winter.

How are plants alike and different from their parents

Migrant workers who fill employment needs in their host country often send remittances to their home countries

The hypothetical island country of gilder lies in the mediterranean sea off the coast of france. demographers have studied gilder for the past 50 years. at the beginning of the study, gilder had a population of 20 million. the demographers have measured birth and death numbers, as well as immigration and emigration numbers, as shown in the data table. from the data, calculate the population of gilder for each 10-year period by filling in the population (no) and population (nt) columns in the data table. use this formula to do your calculations: population size: nt = no + (b + i) – (d + e)initial population = 20,000,000