Hich word group is a complete sentence?

a.
birds nest in the tree.

b.
an old barn with a tractor inside.

c.
six inches of water in the basement.

d.
lindsay's best friend, katie.

Read the excerpt from elie wiesel’s all rivers run to the sea. why were those trains allowed to roll unhindered into poland? why were the tracks leading to birkenau never bombed? i have put these questions to american presidents and generals and to high-ranking soviet officers. since moscow and washington knew what the killers were doing in the death camps, why was nothing done at least to slow down their “production”? that not a single allied military aircraft ever tried to destroy the rail lines converging on auschwitz remains an outrageous enigma to me. birkenau was “processing” ten thousand jews a day. stopping a single convoy for a single night—or even for just a few hours—would have prolonged so many lives. based on the paragraph, the author would most likely agree that it is best to avoid confrontation at all costs. people need to be proactive when they witness an injustice. countries should remain neutral to keep alliances strong. moscow and washington are to be blamed for the holocaust.