The correct options are
A Skandagupta successfully defeated the Hunas.
C The last known Gupta ruler was Vishnugupta.
Skandagupta successfully defeated the Hunas, but they again came with a bigger army after 470 CE, the year when Skandagupta died. They lost many and won some of the wars. The Gupta empire was under great strain due to repeated invasions of the Hunas, and as the Gupta rule weakened, the provincial governors and samantas started to try their luck at independence. The Gupta empire, under all this pressure, ultimately crumbled around 550 CE, with the last recognised ruler being Vishnugupta.