The hyperconjugative stabilities of tert-butyl cation and `2`-butene, respectively, are due to
A. `sigmararrp` (empty) and `sigmararrpi^(**)` electron delocalisations.
B. `sigmararrsigma^(**) and sigmararrpi` electron delocalisations.
C. `sigmararrp` (filled) and `sigmararrpi` electron delocalisations.
D. p (filled) `rarr sigma^(**) and sigma rarrpi^(**)` electron delocalisations.
