Ecological succession refers to the regular replacement process of biological communities on the same site, and is divided into two types: primary succession and secondary succession. In the past, there was no vegetation, or there was vegetation but it was completely destroyed. The succession that begins on the bare ground where the soil no longer exists is called primary succession; the succession that begins where the original vegetation has been destroyed but still retains soil and plant propagules is called secondary succession The biological community that has undergone secondary succession tends to return to its pre-destructive form. According to the above definitions, Which of the following situations that may lead to secondary succession are:. ['Plant seeds cultivated by human beings using genetically modified technology are sprinkled into the forest.', 'Volcanic magma covers the entire island after an island volcano erupts.', 'When the forest was repeatedly cut down, it evolved into a sparse grassland.', 'After the dam is completed, the downstream lakes dry up, and most of the vegetation along the lake is dead.']