In the story, “emma” by jane austen it says “but it was a black morning’s work for her” what does it mean?

Has led many to wonder if being a vegan is both healthy and sustainable for the long term. "vegans get 100% of their daily protein needs from such foods as soy derivatives, bulgur wheat, lentils, nuts, and beans," says mikel rollah, director of veganism now! many opponents of veganism claim that the vegan diet lacks protein, but this is simply not true. what is wrong with the quotation in this example?