The correct option is C a, c
Equivalent fractions are fractions that represent the same part of the whole.
The fraction of shaded parts in figure a is 13.
The fraction of shaded parts in figure b is 28=2÷28÷2=14.
The fraction of shaded parts in figure c is 26=2÷26÷2=13.
The fraction of shaded parts in figure d is 27.
Hence, figures a and c represent equivalent fractions.