Within measurement systems, identify which legacy system's fundamental units most closely match the base set adopted in the International System of Units (S.I.).

Introduction / Context:
S.I. (Système International d’Unités) evolved from earlier metric systems. Recognizing which legacy system aligns with S.I. helps avoid confusion when converting older textbooks, codes, or calculation notes to modern standards in engineering and science.

Given Data / Assumptions:

• S.I. base units include metre (m), kilogram (kg), and second (s) among others.
• Legacy systems listed include C.G.S. (centimetre–gram–second), F.P.S. (foot–pound–second), and M.K.S. (metre–kilogram–second).
• The question asks which is the 'same as' the fundamental set now used by S.I. for length, mass, and time.

Concept / Approach:

While S.I. adds more base quantities (electric current, thermodynamic temperature, amount of substance, luminous intensity), the core mechanical trio in S.I. is metre, kilogram, and second—exactly the M.K.S. set. Thus, M.K.S. is the historical predecessor most consistent with S.I. fundamentals for mechanics.

Step-by-Step Solution:

Verification / Alternative check:

Dimensional formulae in mechanics (e.g., force = mass * acceleration) remain unchanged; only the base unit magnitudes differ, confirming the natural continuity from M.K.S. to S.I.

Why Other Options Are Wrong:

• C.G.S.: Uses centimetre and gram; not the S.I. base magnitudes.
• F.P.S.: Uses imperial units (foot, pound), not metric.
• None of these / gravitational units: Do not directly match the S.I. mechanical base set.

Common Pitfalls:

• Assuming C.G.S. is 'the same' as S.I. because both are metric; they are related but scaled differently.
• Confusing kilogram-force (kgf) with kilogram (kg) mass; S.I. force unit is the newton (N).

Final Answer:

M.K.S. units