Mitosis and Colchicine
The question is asking which is NOT true.  You are correct that C is true - very few cells should be found in anaphase or telophase.

D is also true.  When spindle fibres are dissolved, chromosomes/chromatin would not be tightly bundled or packed in the cell and it would be easier to see them with an acetoorcein stain.

A and B are trick answers.  In a regular tissue, most cells are in interphase at any given time.  Interphase is the regular functioning period for the cell.  

However, the question is referring to onion root tips which are primarily comprised of actively dividing cells (meristem tissue). The colchicine would affect most cells and most cells would be found arrested in the metaphase.  http://w3.marietta.edu/~biol/introlab/Onion%20root%20mitosis.pdf

Therefore for onion root tips treated with colchicine, most cells are not found in interphase.  A is the correct answer.