12. On average, what is the thickness of Saturn's rings? a. about ten millimeters thick b. about ten centimeters thick c. about ten meters thick d. about ten kilometers thick

## Step 1<br />The problem is asking for the average thickness of Saturn's rings. The options provided are: about ten millimeters thick, about ten centimeters thick, about ten meters thick, and about ten kilometers thick.<br />## Step 2<br />The correct answer is "about ten kilometers thick". This is based on the information provided in the explanation, which states that the rings of Saturn are composed of billions of particles, ranging in size from tiny dust grains to objects as large as mountains. These particles are spread out over a large area, with the average thickness of the rings being about ten kilometers.<br />## Step 3<br />The other options, such as ten millimeters, ten centimeters, and ten meters, are too thin to represent the thickness of Saturn's rings. Therefore, the correct answer is "about ten kilometers thick".