Hypothesis: homologous structures are evidence of a common ancestor ? why is this correct ?

Yes, because homologous structures are different structures we have that other different organisms might have. humans and monkeys both have arms, although they are completely different species, this can tell scientists that they could have shared a common ancestor in the past, and may have evolved

Humans can affect weathering and erosion in several ways.  humans cause  increases in acid rain and pollution, which increase the amount of  weathering  agents in the air and water, and then on land.for an easy answer: 1) acid rain2) pollution