How does a digital signal differ from an analog one, and why does that make it robust?

Select one answer.

• A digital signal is only ever one of two states (HIGH/LOW); a wide voltage range counts as each state, so the noise margin lets it shrug off noise and drift.
• A digital signal varies continuously and carries information in its exact voltage.
• A digital signal has no voltage at all, only current.
• A digital signal is more sensitive to noise than an analog one.