Grade 12Cell Division Questions! Please help

In a human cell cycle, the event that occur before mitosis begins and the event that occurs at or near the completion of mitosis are, respectively,
a) cytokinesis and crossing over
b) replication of DNA and synapsis
c) crossing over and synapsis
d) replication of DNA and cytokinesis

Which expression of chromosome content represents a somatic cells in individuals with trisomy disorders such as Down Syndrome?
a) 2n-1
b) n+1
c) 2n+1
d) n-1

A human with Klinefelter Syndrome has 47 chromosomes and has the XXY chromosome set instead of XY. From what does this abnormality result?
a) The process of mitosis does not occur properly
b) an error in replication produces an extra X chromosome
c) crossing over results in the formation of an extra chromosome
d) Nondisjunction occurs in either the formation of the sperm or the egg