You inject an antibody against the protein tubulin into a living animal cell. After the injection, the cell begins mitosis, but the chromosomes do not become attached to the spindle; in fact, there is no spindle. The contractile ring does, however, form. What do these results mean?

The mitotic spindle was “ blocked ” by the action of the antibodies that bind to tubulin.

Explanation:

The tubulin heterodimers consist of α- or β-tubulin structures that form the microtubules, which represent the cytoskeletal of eukaryotic cells. During mitosis, the microtubules are arranged in order to form the mitotic spindle, this structure is critical for the segregation of homologous chromosomes during Anaphase.

Interphase microtubules are required for attaching chromosomes in the middle of the cell during its division, thereby it is expected that the antibodies bind to these microtubules during this process.

The contractile ring is formed by approx. 20 actin filaments that encircle the middle of dividing cells, thereby it is expected that these antibodies are specific of tubulin heterodimers.

it's c. (to reduce the greenhouse effect/carbon gasses)