A) "anyone" is syntactically singular, hence: has anyone…?
C) It boils down to how we make a question with the verb to be, as opposed to how we make a statement.
If it´s any indication of how to make a question, the following passage from the text gives a hint:
Are there other intelligent forms of life out there—or are we more likely to find something much simpler?
D) How many planets have to support life?
The natural way would be “how many planets support life?” “have to” is used to express the fact that something being necessary, required or that must happen.
The question, no doubt, is about not the number of planets that support life. So, it has nothing to do with something being necessary/required or having to happen.