用that，what，whether填空，并说出其引导的从句在句子中充当的成分。
_______ it was to become was uncertain until between 4.5 and 3.8 billion years ago when the dust settled into a solid globe.
The earth became so violent that it was not clear ________ the shape would last or not.
_______ is even more important is that as the earth cooled down, water began to appear on its surface.
_______ many scientists believe is that the continued presence of water allowed the earth to dissolve harmful gases and acids into the oceans and seas.
It was not immediately obvious _______ water was to be fundamental to the development of life.
So _______ life will continue on the earth for millions of years to come will depend on whether this problem can be solved.
结论： what引导从句，并在从句中充当________。（1,3,4）
that引导从句，但在从句中________成分，也无意义。（5）
________引导从句，在从句中不充当成分，但是有“是否”的意义。（2,6）