To answer this question, we need to understand what makes a requirement testable. A testable requirement is one that can be objectively measured or verified.
Let's go through each option to determine which one is testable:
Option A) The system shall be user friendly - This requirement is not testable because "user friendly" is a subjective term and does not have a clear and objective measure.
Option B) The safety-critical parts of the system shall contain 0 faults - This requirement is not testable because it is impossible to guarantee that a system will have zero faults. It is unrealistic to expect any complex system to be completely free of faults.
Option C) The response time shall be less than one second for the specified design load - This requirement is testable. Response time can be objectively measured and verified using performance testing or load testing techniques.
Option D) The system shall be built to be portable - This requirement is not testable because "portable" is a subjective term and does not have a clear and objective measure.
Based on the above analysis, the correct answer is C) The response time shall be less than one second for the specified design load. This requirement is testable because it can be objectively measured and verified.