20. What do scientists use to provide evidence that the earth has a solid inner core and a liquid outer core?
(1 Point)
A) drilling into the mantle
B)seismic wave
C) radar
D)x-rays
21. The layer of the atmosphere closest to the surface of the earth is called the
(1 Point)
A) Stratosphere
B)exosphere
C)mesosphere
D) troposphere

explanation:

okay now i don't know this but for the pints nothing else to say bye

desert perennials often survive by remaining dormant during dry periods of the year, then springing to life when water becomes available. most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly.