Machine Language is used as a programming language in first generation computers.

Explanation:
First generation computers, also known as vacuum tube computers, were developed in the 1940s and 1950s. These computers were built using vacuum tubes and were the first electronic digital computers. They were programmed using machine language.

Machine language is the lowest-level programming language that computers can understand directly. It consists of a series of binary instructions that are executed by the computer's hardware. Each instruction represents a specific operation such as addition, subtraction, or comparison.

Here is an explanation of why the other options are not correct:

a) FORTRAN (Formula Translation) is a high-level programming language developed in the 1950s. It was not used in first generation computers as they were developed before the creation of FORTRAN.

b) COBOL (Common Business-Oriented Language) is another high-level programming language that was developed in the late 1950s and early 1960s. Like FORTRAN, it was not used in first generation computers.

c) BASIC (Beginner's All-purpose Symbolic Instruction Code) is a high-level programming language that was developed in the 1960s. It was also not used in first generation computers.

Therefore, the correct answer is option D - Machine Language, as it was the only programming language used in first generation computers.

In summary, first generation computers were programmed using machine language, which is the lowest-level programming language consisting of binary instructions. The other options (FORTRAN, COBOL, and BASIC) were high-level programming languages developed after the first generation of computers.