a - 

Each part is one-third

b - 

Each part is one-half

c - 

Each part is one-quarter

Each part is one-third when - 

the whole has been divided into 3 equal parts.

Each part is one-half when - 

the whole has been divided into 2 equal parts.

Each part is one-quarter when - 

the whole has been divided into 4 equal parts.

a - 

$$ \frac{1}{4} $$

b - 

$$ \frac{1}{3} $$

c - 

$$ \frac{1}{2} $$

$$ \frac{1}{2} $$ - 

one-half

$$ \frac{1}{3} $$ - 

one-third

$$ \frac{1}{4} $$ - 

one-quarter

a - 

$$ \frac{1}{4} $$

b - 

$$ \frac{1}{2} $$

c - 

$$ \frac{1}{3} $$