Fimbriae and pili differ in that
a) pili are used for attachment to surfaces.
b) pili are used for motility.
c) pili are used to transfer dna.
d) pili are used for transfer of dna and motility.
e) there are only one or two pili per cell.

The correct option is D.  Pili are used for transfer of DNA and motility.

Pili are responsible for twitching like motility of bacteria. Fimbriae on the other hand have nothing to do with motility.

Pili serve the function of DNA transfer while fimbriae help in only cell surface attachment. The number of fimbriae in a bacterial cell may vary from 200 to 400 whereas the number of pili may vary from 1 to 10 per cell.

It may also be noted that fimbriae are found in both gram positive and gram negative bacteria while pili are found in only gram negative bacteria.