A fold observed in layers of sedimentary rock most likely resulted from the OPTIONS:
- cooling of flowing magma.
- converging of crustal plates.
- deposition of river sediments.
- solution of carbonate minerals.
A: converging of crustal plates.

Many cars are equipped with a catalytic converter, a device that helps remove hydrocarbons and oxides from car exhaust. As a result, this device helps to OPTIONS:
- increase the production of ozone.
- decrease the production of smog.
- increase the emission of nitrogen.
- decrease the emission of carbon dioxide.
A: decrease the production of smog.

Which activity is directly regulated by neurons? OPTIONS:
- production of sex cells
- the beating of the heart
- the rate and the shape of bone growth
- levels of sugar in the blood
A: the beating of the heart

If a book sitting on a flat table starts to move horizontally, it is most likely moving because OPTIONS:
- a balanced force is being applied.
- a frictional force is being exerted.
- an unbalanced force is being applied.
- a gravitational force is being exerted.
A:
an unbalanced force is being applied.