China Was Susceptible to Frequent Earthquakes, So a Seismograph Invented

China was susceptible to frequent earthquakes, so a seismograph invented under the Han Dynasty used which of these mechanisms?

A) suspended weight moves a lever which drops balls into a ceramic frog's mouth
B) a magnetic arm moves a writing instrument across a piece of parchment
C) specially colored wooden dragons float in a vat of colored water
D) two chemicals are separated inside an urn; when shaken they produce a distinct glow