An underwriting agreement contains a 'market out' clause. Under which circumstance would this clause most likely be invoked?

Why B — When a material adverse change occurs in the issuer's business or in market conditions between pricing and closing that makes the offering impractical

A market out clause allows the underwriters to terminate their purchase obligation if certain adverse events occur between pricing and closing, such as a material adverse change in the issuer's condition, a significant disruption in the financial markets, or the outbreak of hostilities. This provision protects underwriters from being forced to close a transaction when circumstances have materially changed since the agreement was executed. The clause is standard in virtually all firm commitment underwriting agreements and is heavily negotiated between issuers and underwriters.