Define permafrost.
a. water below the surface of the tundra stays frozen all year long
b. the frozen soil in mountain highlands
c. rainwater that collects on rocks after a cold rainstorm
d. the dew droplets that freeze at high altitudes

What group has historically made up the largest portion of immigrants in mexico?

Plants can have a positive and negative effect on the rate of weathering

Brian's school locker has a three-digit combination lock that can be set using the numbers 5 to 9 (including 5 and 9), without repeating a number. the probability that the locker code begins with a prime number is %. the probability that the last digit of the locker code is an odd number is %.