a) An asteroid
d) Climate change
I'd say the majority of evidence point towards asteroid impact as can be seen in regards to the Chicxulub crater in the Yucatán Peninsula in Mexico
and the after effects of this impact. In addition to this around the world there is something known as the 'Iridium anomaly' where there is an unusual abundance of the element iridium in strata of this age, around the 65 million year mark, Iridium is a fairly scare element in the earth and is found in concentrations of nearly one hundred times the expected amount in deposits of this age. The most widespread theorgy at the moment attributes this to meteorite collisions with the earth.
Wasn't the asteroid theory proven in 2010 or 2011?
It is almost certain that it was an asteroid, although this would probably have triggered volcanic activity, tsunamis and massive climate change due the the dust cloud it would have thrown up. The dinosaurs were certainly wiped out by a mixture of them all.