Final answer:
The origin of the universe is attributed to the expansion of a singularity in spacetime known as the Big Bang, corroborated by galaxy recession, cosmic microwave background radiation, and the abundances of certain light elements.
Step-by-step explanation:
The trigger for the origin of the universe is widely accepted to be A. The expansion of a singularity in spacetime, known as the Big Bang. This concept is supported by observations such as the recession of galaxies resembling the remnants of a vast explosion, and the detection of the cosmic microwave background (CMB) radiation, which is the redshifted afterglow of the Big Bang. Extensive evidence, including redshifts of galaxies indicating universe's expansion, supports the Big Bang theory, which posits the universe began approximately 13 to 15 billion years ago from a highly dense and hot initial state.
Additional confirmations of the Big Bang theory include the abundance of light elements such as deuterium, helium, and lithium, which match predictions from the theory. The early phase of rapid expansion, known as inflation, was followed by a period of deceleration due to gravitational pull from closely packed galaxies, and later an accelerated expansion attributed to dark energy. The Big Bang theory remains central to our understanding of cosmological history and continuous research aims to explore the enigmas such as the precise nature of the singularity and the cause of inflation.