Simplify the following text for a Grade 11 native English-speaking person.
Original: The proportion of C-types may actually be greater than this , because C-types are much darker than most other asteroid types except D-types and others common only at the extreme outer edge of the Main Belt .
Simplified: The amount of C-types may actually be higher than this , because C-types are much darker than most other asteroid types except D-types and others common only at the extreme farther edge of the Main Belt .