Final answer:
In 'Harry Potter and the Order of the Phoenix', Umbridge forced Harry to write 'I must not tell lies' with a magical quill, marking his hand as punishment. The correct answer is A) I will not speak ill of Dolores Umbridge.
Step-by-step explanation:
The phrase that Dolores Umbridge made Harry Potter write with his own blood in detention was 'I must not tell lies.' This cruel punishment was one of the ways she enforced her authority as the Defence Against the Dark Arts (DADA) teacher in 'Harry Potter and the Order of the Phoenix'.
The magical quill used for this punishment caused the words to be etched onto the back of Harry's hand, scarring him temporarily.
This punishment is known as the Blood Quill, in which the writing instrument is enchanted to cut into the writer's hand as they write. Umbridge used this cruel and unusual method of punishment to ensure obedience and control over her students.