Here are the answers for the questions based on the advertisement you provided:

**Question 10:**
The correct answer is **C. a**
*Explanation:* "a" is used before singular nouns that begin with a consonant sound.

**Question 11:**
The correct answer is **D. in**
*Explanation:* "in" is appropriate for indicating publication within a specific medium like a newspaper.

**Question 12:**
The correct answer is **A. a qualification**
*Explanation:* "a" is used here because "qualification" is singular and begins with a consonant sound.

So the completed sentences would be:
- "Draft (10) **a** suitable advertisement..."
- "...to be published in the classified columns (11) **in** a national newspaper..."
- "...giving all the necessary details of (12) **a qualification**..."