The term "sixth mass extinction/sixth extinction" is often mentioned in the news in the context of the discussion of

The term "sixth mass extinction/sixth extinction" is often mentioned…

Widespread monoculture practices in agriculture and large-scale commercial farming with indiscriminate use of chemicals in many parts of the world that may result in the loss of good native ecosystems.
Fears of a possible collision of a meteorite with the Earth in the near future in the manner it happened 65 million years ago that caused the mass extinction of many species including those of dinosaurs.
Large scale cultivation of genetically modified crops in many parts of the world and promoting their cultivation in other parts of the world which may cause the disappearance of good native crop plants and the loss of food biodiversity.
Mankind's over-exploitation/misuse of natural resources, fragmentation/loss of natural habitats, destruction of ecosystems, pollution and global climate change.

Answer

(a) Monoculture and chemical-intensive farming do harm biodiversity, but the term "sixth mass extinction" is not specifically used for this alone. Verdict: Incorrect.
(b) This refers to a possible future meteorite impact like the one linked to the fifth mass extinction; the sixth extinction is not about an expected asteroid event. Verdict: Incorrect.
(c) GM crops and crop biodiversity loss are debated issues, but "sixth mass extinction" refers more broadly to species extinction across ecosystems, not specifically to GM cultivation. Verdict: Incorrect.
(d) The sixth mass extinction is widely used for the ongoing human-driven biodiversity crisis caused by habitat loss, overexploitation, pollution, invasive species and climate change. Verdict: Correct.