Companies$($e$.$g$.,$ Salesforce.com$)$ that lease their software over the Internet are engaged in$\_\_\_\_\_\_\_\_\_\_,$ which represents a type of cloud computing.

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Part $1$

A$.$

Simple Storage Service$($S$3)$

B$.$

Azure as a service$($AaaS$)$

C$.$

platform as a service$($PaaS$)$

D$.$

software as a service$($SaaS$)$

E$.$

infrastructure as a service$($IaaS$)$