"Sra. Domínguez, ¿por cuánto tiempo estaban enfermos sus hijos?" "Estaban enfermos _____ casi diez días."

a. para
b. por
c. hasta
d. desde

i THINK por (B) fits best, seeing the definition that SraJMcGin gave yesterday.
is that right?

Yes, you are correct. The correct answer in this case is "por" (b).

To determine the correct answer, we can look at the information provided in the question and the options given. The question asks about the duration of the illness of Sra. Domínguez's children. In the response, it is stated "Estaban enfermos _____ casi diez días," which means "They were sick _____ almost ten days."

The word "por" in Spanish is commonly used to express duration, in this case, the length of time the children were sick. Therefore, the correct answer is "por" (b), as it accurately conveys the intended meaning.