观察下列各式:

1×3+1=4=2²， 2×4+1=9=3²， 3×5+1=16=4²，4×6+1=25=5²，

…….

请将你所发现的规律用含字母n的式子表示出来:________;

It was not immediately obvious _____ water was to be fundamental to the development of life.

A．what

B．that

C．when

D．why