I've read the sentence below in my grammar book and I don't see the difference between <b>such a</b> and <b>a so</b> in this example.<br/><br/>Mr. Jones is very ill and his daughter hasn't visited him for ......... long time.<br/><br/>a) such a<br/>b) a so<br/><br/>The correct answer is supposed to be <b>a</b>, but why? If the b choice was <b>so</b> (without the article), would it be correct?<br/><br/>Also, I am not sure when we use <b>such a</b> and when <b>such</b>. Could someone help me, please, clear this up?