Meaning: 'Complex' refers to something that is made up of many different parts that are interconnected and not straightforward.

Wrong options:

• crime: The word 'crime' is a noun that refers to an illegal act, which does not fit the context of describing biological systems.
• organisation: The word 'organisation' is a noun that refers to the arrangement or structure of something, but it does not describe the nature of engineering in this context.
• methods: The word 'methods' is a noun that refers to ways of doing something, which does not appropriately describe the nature of engineering in biological systems.
• genuine: The word 'genuine' is an adjective that means authentic or real, which does not fit the context of describing the complexity of engineering.

Correct answer: organisation

Explanation: The term 'organisation' is a noun that refers to the structured arrangement of components within a system. It fits grammatically as it serves as the subject of the clause, indicating that biological systems have a specific structure resulting from natural selection.

Meaning: 'Organisation' refers to the way in which parts are arranged or structured within a system.

Wrong options:

• crime: The word 'crime' does not fit as it refers to illegal acts and is unrelated to the concept of biological systems' structure.
• complex: The word 'complex' is an adjective and cannot function as a noun in this context, making it grammatically incorrect here.
• methods: The word 'methods' refers to approaches or techniques, which does not accurately describe the structural aspect of biological systems.
• functions: The word 'functions' is a noun that refers to the roles or purposes of something, but it does not describe the arrangement or structure of biological systems.
• genuine: The word 'genuine' does not fit as it describes authenticity rather than the structural organization of systems.

Correct answer: functions

Explanation: The word 'functions' is a noun that refers to the specific roles or purposes that biological systems serve. It fits grammatically as it completes the idea that these systems should have roles that aid in survival and reproduction, aligning with the context of natural selection.

Meaning: 'Functions' refer to the specific activities or roles that something is designed to perform.

Wrong options:

• crime: The word 'crime' does not fit as it refers to illegal acts, which is unrelated to the roles of biological systems.
• complex: The word 'complex' is an adjective and cannot serve as a noun in this context, making it grammatically incorrect here.
• organisation: The word 'organisation' refers to the arrangement of parts, but it does not convey the idea of roles or purposes in this context.
• methods: The word 'methods' refers to techniques or approaches, which does not accurately describe the roles of biological systems.
• genuine: The word 'genuine' does not fit as it describes authenticity rather than the functional roles of biological systems.