Explanation:

Computers fundamentally operate on machine language, which is the lowest-level programming language consisting of binary code (sequences of $0$s and $1$s). These binary instructions are directly executed by the computer's central processing unit (CPU) without the need for translation. All high-level programming languages must be compiled or interpreted into machine language before a computer can understand and execute them. (a) American language: Incorrect. This is a natural human language, not understood by computers. (b) Machine language: Correct. This is the only language directly executable by the CPU. (c) Secrect language: Incorrect. This is not a recognized computer language term. (d) All of these: Incorrect, as only machine language is directly understood. (e) None of these: Incorrect, as (b) is the correct option.