What is an advantage of split injection versus splitless injection in gas chromatography?

$($A$)$ Split injection is more sensitive

$($B$)$ Split injection provides better resolution.

$($C$)$ Split injection provides faster separations.

$($D$)$ Split injection allows two detectors to be uscd.

Polar solutes were separated by HPLC using a bonded phase containing polar diol functional groups $-CH(OH)C{H}_{2}OH$ How would the retention times be affected if the mobile phase were changed from $40\%(\frac{v}{v})$ to $60\%(\frac{v}{v})$ acetonitrile in water?

$($A$)$ retention times would increase

$($B$)$ retention times would decrease

$($C$)$ retention times would not change

$($D$)$ cannot predict without structures of solutes