The word "it" (Line 3, Para. 6) probably refers to ______.

A．To learn whether trees can still absorb carbon dioxide under extreme conditions.
B．To get more oxygen from these trees.
C．To evaluate the maximum carbon dioxide that trees can absorb.
D．To see the growth rate of these trees.

A．Demonstrating the serious weather condition around Lake Chad.
B．Introducing people's activity around Lake Chad.
C．Analyzing of the factors that cause water decreases in Lake Chad.
D．Introducing scientists' work about water condition in Lake Chad.