Final answer:
The expressions 'abc', 'a + b + c', and 'ab/c' must be irrational.
Step-by-step explanation:
To determine which of the given expressions must also be irrational, we need to understand the properties of irrational numbers.
An irrational number is a number that cannot be expressed as a fraction or a ratio of two integers. It cannot be written as a terminating or repeating decimal.
Given three positive irrational numbers, the following expressions must also be irrational:
- abc: The product of three irrational numbers will also be irrational, as the product of rational and irrational numbers is irrational.
- a + b + c: The sum of three irrational numbers can also be irrational, as the sum of rational and irrational numbers can be irrational.
- ab/c: The division of two irrational numbers can also be irrational.
Therefore, the correct answers are options A, B, and C.