A computer program that translates a program statement by statement into…

Concept: A language translator is a system program that converts source code written by a programmer into machine language that the processor can execute. Translators are distinguished by the unit of code they handle at one time and by what they leave behind: one kind translates the complete program before execution and stores a separate machine-code file, while another kind works on a single statement at a time and executes it immediately, storing no separate machine-code file.

Application: The stem fixes the unit of translation as "statement by statement" into machine language. The term whose defining behaviour is exactly that per-statement unit is the interpreter: it converts one source statement, executes it, and only then reads the next statement. The answer is therefore Interpreter.

Cross-check: how each offered term is defined:

• Compiler — translates the entire source program before it is run, producing a separate object or executable file that is executed afterwards as a standalone unit.

• Simulator — reproduces the behaviour of one system (a machine, a device, or an environment) on another platform, so that its operation can be observed or tested there.

• Translator — the generic category name for any system program that converts code written in one language into an equivalent form in another language; it names the whole family of such tools rather than one member of it.

• Interpreter — converts one source statement into machine language and executes it immediately, then moves on to the next statement, without producing a separate executable file.

Only the interpreter is defined by the per-statement unit that the stem describes, while "translator" names the family that contains it. The program that translates a program statement by statement into machine language is the interpreter.