The global financial system is [1] on a network of interdependent institutions whose failure can trigger cascading consequences. The 2008 crisis demonstrated how the [2] of complex financial instruments — particularly mortgage-backed securities — could mask systemic risk until it became [3]. Regulatory bodies had largely failed to [4] with the pace of financial innovation, leaving oversight frameworks dangerously outdated. [5] banks were allowed to operate with insufficient capital reserves, the stage was set for catastrophic collapse. Governments were ultimately compelled to bail out the failing institutions, a decision that provoked considerable public controversy. The episode exposed a fundamental flaw in the prevailing doctrine of self-regulating markets. Economists now argue that financial stability is a public good that cannot be left entirely to market forces.

1. Blank [1]
   • A. built ✓
   • B. founded
   • C. predicated
   • D. based

   The sentence requires a verb that collocates with 'on' to describe a system resting on a foundation. 'Built on' is the most natural and widely used phrasal verb for a system whose structure rests upon or is constructed from something else. 'Based on' is equally common, but 'built on a network' is more architectural and vivid. 'Founded on' is used for institutions or ideas at their origin. 'Predicated on' is used for logical arguments, not physical/institutional structures, and is too philosophical for this analytical economic context.

2. Blank [2]
   • A. expansion
   • B. spread
   • C. proliferation ✓
   • D. growth

   The blank describes the multiplication of complex financial instruments. 'Proliferation' specifically means a rapid and often uncontrolled increase in number — it carries a negative connotation of excessive multiplication, which is precisely the problem being described. 'Proliferation of financial instruments' is the standard phrase in financial regulation discourse. 'Expansion' and 'growth' suggest healthy, planned increase. 'Spread' is used for ideas, diseases, or geographic diffusion — not for the increase in types of instruments.

3. Blank [3]
   • A. unmanageable
   • B. critical
   • C. acute
   • D. untenable ✓

   The sentence states that systemic risk was masked 'until it became ___3___' — meaning until the situation could no longer be concealed or sustained. 'Untenable' means impossible to defend, maintain, or continue — a state that forces revelation or collapse. It is the most precise word for describing the point at which a masked risk becomes impossible to sustain. 'Unmanageable' describes difficulty of control. 'Critical' means dangerously serious. 'Acute' means severe and sudden. Only 'untenable' captures the sense of a situation that simply cannot be held together any longer.

4. Blank [4]
   • A. deal
   • B. keep up ✓
   • C. cope
   • D. contend

   The blank precedes 'with the pace of financial innovation' — testing the correct phrasal verb. 'Keep up with' is the precise phrasal verb meaning to match the speed or rate of something else. It perfectly captures the idea that regulators could not maintain pace with rapid financial innovation. 'Cope with' means to manage or handle difficulties — it implies dealing with something difficult, not specifically matching a pace. 'Deal with' is too generic. 'Contend with' means to struggle against — it implies active competition rather than a failure to match speed.

5. Blank [5]
   • A. Once ✓
   • B. Because
   • C. When
   • D. Since

   The sentence reads '___5___ banks were allowed to operate with insufficient capital reserves, the stage was set for catastrophic collapse.' The conjunction must establish a temporal-conditional relationship: the moment the condition existed, the consequence became inevitable. 'Once' is the most precise choice — it means 'as soon as' or 'at the moment that', implying immediate and irreversible consequence. 'When' is a general temporal connector. 'Because' and 'Since' establish causation rather than the precise moment of consequential entry that 'once' provides.