The correct answer is Increase speed and agility because:

• Speed and agility refers to the ability to rapidly provision and deploy resources, which directly supports the requirement to "develop, test, and launch an application quickly"
• This cloud computing advantage allows organizations to reduce the time from idea to implementation significantly
• The other options, while valid cloud benefits, don't specifically address the speed requirement:
  • Stop guessing capacity focuses on resource planning and optimization
  • Trade fixed expense for variable expense relates to cost management and payment models
  • Achieve economies of scale deals with cost efficiency through large-scale operations

In AWS Cloud, speed and agility is achieved through on-demand resource provisioning, automated deployment tools, and scalable infrastructure that enables rapid development and testing cycles.