Which type of mining causes large amounts of sediment and debris to choke rivers and streams as its main environmental impact?

In the following diagram, four different index fossils are labeled: which of the labeled fossils comes from the oldest organism? a b c d

Given: circle a externally tangent to circle b. how many possible common tangents to circles a and b can exist? 2 3 4

All of the following actions are examples of civil disobedience, except a.) refusing to pay an unfair tax b.) refusing to use government services c.) participating in a protest march d.)planning a riot to destroy a government riot