The appropriate descriptors of geometric sequences are ...
... B) Geometric sequences have a common ratio between terms.
... D) Geometric sequences are restricted to the domain of natural numbers.
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The sequences may increase, decrease, or alternate between increasing and decreasing.
If the first term is zero, then all terms are zero—not a very interesting sequence. Since division by zero is undefined, the common ration of such a sequence would be undefined.
There are some sequences that have a common difference between particular pairs of terms. However, a sequence that has the same difference between all adjacent pairs of terms is called an <em>arithmetic sequence</em>, not a geometric sequence.
Any sequence has terms numbered by the counting numbers: term 1, term 2, term 3, and so on. Hence the domain is those natural numbers. The relation describing a geometric sequence is an exponential relation. It can be evaluated for values of the independent variable that are not natural numbers, but now we're talking exponential function, not geometric sequence.
