It would be D because would be small and you wouldn't feel it. For answer A, the scientist could feel it. For answer B, you can kind of feel it or feel it. For C, It can definitely feel it. So the answer would be d.
Earthquakes occur as energy is released from tectonic plates; these are commonly measured using a scale from 1 to 8 or 9. In this scale, earthquakes with a magnitude of 2 or less (< 2.0) are considered microearthquakes only registered by seismograph (an instrument that registers ground movements) but which are not commonly felt by people.
On the other hand earthquakes between 3.0 and 4.0 (minor earthquakes) can be felt by some people and earthquakes from higher magnitudes including moderate, strong, major and great earthquakes (from 4 to 8or 9) are felt by most people and also lead to damages on infrastructures that increases with magnitude. Thus, if a seismograph records an earthquake but scientists do not feel it has a magnitude < 2.0.
