sat writing mc explanations please!

[silverturtle]

<p>

46. In the past, children were content to entertain themselves with kitchen pots and balls of (twine, rather than high-priced electronic toys).
    a. twine, rather than high-priced electronic toys
    b. twine; now they want high-priced electronic toys</p>

<p>the answer is b, but can someone expalin why a is wrong? thanks!

</p>

<p>The comma before “rather” indicates that everything after “rather” is to form a clause; choice (A) is not a clause.</p>