Question

a chromatid is attached to a spindel fiber by the

Answer 1

Here's a picture of a duplicated chromosome:
http://img.tfd.com/dorland/arm_chromosome.jpg

Now, try to remember mitosis.
When the little strings (the spindle fibers) come out, they attach to the chromosomes, right in the middle.
You see that round, yellow part in the middle? It's called the "centromere."
And the centromere is where the spindle fibers attach to the chromosome.