MacConkey agar uses lactose as a differential agent, however it is not as specific as an EMB test in terms of types of coliforms detected. This makes the MacConkey test useful in a clinical setting but not necessarily useful in environmental microbiology. Could MacConkey agar be altered by using a carbohydrate other than lactose for differentiation

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weathering - colorado river carves land in arizona to form the grand canyon. cracks form in a sandstone wall surrounding a house. a marble statue near the science museum is changing color due to rainfall

erosion - after a rainstorm, soil and rock piees litter the roadways. the sand dunes in the sahara desert are changing shape.

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geographic isolation