Final answer:
The form of underwriting where underwriters fully commit to buying all securities is known as Firm commitment underwriting, which differs from best-efforts, standby, and all-or-none underwriting. Option b.
Step-by-step explanation:
The form of underwriting in which the underwriters commit to buy all securities is known as B. Firm commitment underwriting. In this type of agreement, the underwriters guarantee the issuer that they will purchase all the offered shares or securities at an agreed-upon price. They then sell these securities to the public, bearing the risk of not being able to sell them all. This is different from other forms of underwriting such as best-efforts, standby, and all-or-none underwriting, which do not involve this level of commitment from the underwriters.