Which is nor a charticteristic of capillary zone electrophoresis?

$($A$)$ flat flow profile

$($B$)$ separation achieved by a combination of electrophoretic and electroosmotic flow

$($C$)$ capillary columns lacking stationary phase

$($D$)$ required mobile phase gradient for complete separation of complex mixtures

Items $$39$ and $$40$ refer to the isochratic chromatogram below, for which an absorbance detector was used.

$39.$ Which would explain peak $A$ at $4\mathrm{.}5$min having higher concentration than peak B at $6\mathrm{.}4$min $?$

$($A$)$ The molar absorptivity of peak $A$ at $4\mathrm{.}5$min is lower than that for peak B at $6\mathrm{.}4$min.

$($B$)$ Absorbance changes with the extent of dilution due to diffusional broadening.

$($C$)$ Absorbance detectors are mass sensitive$.$

$($D$)$ Longer retained peaks exhibit greater preconcentration at the beginning of the column.

$40.$ What is the resolution of the A and B analytes?

$($A$)0\mathrm{.}65$

$($B$)1\mathrm{.}2$

$($C$)2,1$

$($D$)5$