The correct answer is B, $2,100. Cost basis represents the total amount invested in a security, including reinvested dividends. It is critical for determining capital gains or losses when the investment is eventually sold.

Step 1: Calculate the initial investment. The investor buys 100 shares at $20, resulting in:

100 × $20 = $2,000

Step 2: Calculate the dividend received. The investor receives a $1 per share dividend on 100 shares:

100 × $1 = $100

Step 3: Determine reinvestment. The $100 dividend is reinvested at $25 per share. This purchases:

$100 ÷ $25 = 4 additional shares

Step 4: Adjust cost basis. Even though the investor now owns more shares (104 total), the key point is that reinvested dividends are added to the cost basis because they are treated as new investments. Therefore:

$2,000 (original investment) + $100 (reinvested dividend) = $2,100

The reinvestment price does not change the total cost basis amount—only the number of shares acquired. Thus, the investor’s total cost basis after reinvestment is $2,100, making choice B correct.