Final answer:
The equivalent expression to "3a - 5a + 7a" is "5a" after combining like terms by adding the coefficients, which makes answer choice (a) correct.
Step-by-step explanation:
The question asks which expressions are equivalent to the algebraic expression 3a - 5a + 7a. To find the equivalent expression, we need to combine like terms. Combining like terms means adding or subtracting coefficients of terms that have the same variable. Here, all terms have the same variable a, so we can combine them.
To simplify this expression, we add the coefficients of a: 3 + (-5) + 7, which equals 5a. Hence, the equivalent expression to 3a - 5a + 7a is 5a, which corresponds to answer choice (a).