To determine the increasing order of DNA fragments (A, B, C, D) based on the number of base pairs, we need to understand how gel electrophoresis works. In gel electrophoresis, DNA fragments are separated by size, with smaller fragments moving faster and thus further through the gel than larger ones.

In the provided image, the position of the fragments relative to the wells and the ladder gives us information about their size:

• Fragment A is closest to the bottom, indicating it has the smallest number of base pairs.
• Fragment D is above A, suggesting it has more base pairs than A but fewer than C and B.
• Fragment C is above D, indicating it has more base pairs than D.
• Fragment B is the closest to the wells, meaning it has the largest number of base pairs.

By examining their positions, we can arrange the fragments in increasing order of their size:

• A - Smallest number of base pairs
• D - Greater than A
• C - Greater than D
• B - Largest number of base pairs

Thus, the correct order of fragments from smallest to greatest number of base pairs is A, D, C, B.