The correct option is
D means
Option C: 'Means' means 'an action or system by which a result is achieved'.
It agrees to the given sentence: we can find out more about the shape of the earth by the action of the satellites.
Hence option C is correct.
Option A: 'Quality' refers to 'a property or characteristic'. The word does not contribute to the sentence in meaning.
Option B: 'Sending' leaves the sentence incomplete. The action of 'sending' does not fit the sentence.
Option D: 'Method' refers to a process through which an action is achieved.
The 'satellites' do not equal to a process or method.
Hence these words are not suitable and options A, B and D are incorrect.