Suppose that the number of kinds of lichens at a city park s decreasing each year. what might explain this disappearance?

Each pair of clay balls represents two planetesimals. if each planetesimal is composed of the same material and is separated he the same distance, which pair experiences the frayed gravitational attraction?

Which layer will become saturated first when rain falls?

Which of the following particles always has a positive charge? a. electronb. neutron c. proton d. ion