A repeating decimal: A decimal number with a digit (or group of digits) that repeats forever.
From the options provided,
Option A
0.4 is not a repeating decimal
Option B
0.375 is not a repeating decimal
Option C
0.278278278 is a repeating decimal because 278 is repeating
Option D
0.12222222 is a repeating decimal because 2 is repeating
The answers are options C and D