Impact craters greater than about ___ km diameter have central peaks, and are called 'complex'. A. one B. four C. ten

The impact craters that are classified as 'complex' typically have a diameter greater than a certain threshold. Based on geological surveys and studies of lunar and planetary surfaces, complex craters, which are characterized by features such as central peaks or ringed structures, generally form when the impact is of significant energy, allowing the material to rebound and create these distinctive features.

To answer the question regarding the specific diameter that categorizes these craters:

1. Understanding Impact Craters: Impact craters can be classified as simple or complex depending on their size and structure. Simple craters have a bowl shape and are smaller in size.

2. Characteristic Diameter for Complex Craters: Research indicates that craters larger than about 4 km in diameter start showing complex structures, including central peaks.

Given these points, the correct answer to fill in the blank is:

Final Answer: B. four