**Core Concept**
The question tests the understanding of periodontal involvement in terms of attachment loss. Attachment loss refers to the loss of periodontal ligament and bone support around a tooth, which is a key indicator of periodontal disease.

**Why the Correct Answer is Right**
To find the number of periodontally involved sites, we first need to calculate the total number of sites in the mouth. Since each tooth has 4 sites (mesial, distal, buccal, and lingual), a patient with 28 teeth would have 28 * 4 = 112 sites. Given that 20% of these sites have attachment loss, we calculate 20% of 112, which equals 0.20 * 112 = 22.4.

**Why Each Wrong Option is Incorrect**
**Option A:** This option might be incorrect due to a miscalculation of the total number of sites or the percentage of sites with attachment loss.
**Option B:** Without knowing the exact calculation, it's hard to pinpoint why this is wrong, but it could be due to an error in calculating 20% of the total sites.
**Option C:** Similarly, without the specific numbers, it's difficult to say why this option is incorrect, but it could stem from a mistake in calculating the total sites or the percentage affected.
**Option D:** This option is also incorrect due to a potential miscalculation of the total sites or the application of the percentage.

**Clinical Pearl / High-Yield Fact**
It's crucial to remember that periodontal disease is assessed by evaluating the depth of pockets, the amount of attachment loss, and other factors like bleeding on probing. The percentage of sites involved can help in determining the severity and extent of the disease.

**Correct Answer:** Correct Answer: B. 22.4