Aplasmid . a. can confer antibiotic resistance to a bacterium. b. is a single-stranded circular dna molecule that can undergo horizontal transfer among bacteria. c. is a tool designed in the lab and never found in naturally occurring bacteria. d. always becomes part of the bacterial chromosome during transformation.

The correct answer will be option-A.

Explanation:

The genetic material of a bacteria is organized into a single circular structure called chromosome which is found suspended in the cytoplasm of bacteria.  

In addition to this, bacteria also contain additional double-stranded circular DNA molecule called plasmid.  These plasmid confers survival of the bacteria in the stressful conditions as the genes specific to particular functions are present in the plasmid.

These plasmids are named on the basis of the function they provide like R-plasmid which provide the antibiotic resistance to the bacteria. The plasmid consists of the genes which helps in the transfer of the plasmid as well as the r-determinants which confers antibiotic resistance to the bacteria

Thus, option A is the correct answer.

it would be c. xylem.