Final answer:
Option b, '1≤x≤9', represents the largest interval from 1 to 9, as it includes all numbers within this range and is the only valid compound inequality listed.
Step-by-step explanation:
The question requires us to find a compound inequality using the digits 1 to 9, without repetition, that represents the largest interval. Option b, 1≤x≤9, states that x is greater than or equal to 1 and less than or equal to 9. This compound inequality indeed represents the largest interval among the given options, as it includes all the numbers from 1 through 9. The other options, such as Option c (1≥x≥9) and Option d (1>x>9), do not make mathematical sense because an interval cannot start with a greater number and end with a smaller number, and Option a only represents a single number rather than an interval.