The correct answer is option 'C' - 1 and 3.

Cloud computing is a model for delivering computing services over the internet. It provides access to a wide range of resources, including storage, processing power, and software applications, without the need for users to invest in expensive infrastructure or hardware. There are several key characteristics of cloud computing, and two of them are software as a service mode and a common objective for all users.

1. Software as a Service (SaaS) mode:
Software as a Service is a software distribution model in which applications are hosted by a service provider and made available to customers over the internet. In the context of cloud computing, SaaS allows users to access and use software applications without the need to install or maintain them on their own devices. The applications are typically delivered through a web browser, and users pay a subscription fee to access and use the software.

2. Users should pay scheme:
While it is true that users typically pay for the services they use in cloud computing, this is not a defining characteristic of cloud computing. The payment scheme can vary depending on the specific service provider and the pricing model they offer. Some providers may charge based on a subscription model, where users pay a fixed monthly or annual fee, while others may charge based on usage, where users pay for the resources they consume. Therefore, the statement that users should pay is not a fundamental aspect of cloud computing.

3. Common objective of all users:
One of the key aspects of cloud computing is that it provides a common infrastructure and platform for all users. This means that regardless of the specific requirements or goals of individual users, the underlying infrastructure and services are shared among all users. The cloud computing environment is designed to be scalable, flexible, and accessible to a wide range of users, with the common objective of providing efficient and cost-effective computing resources. This shared infrastructure enables users to access resources on-demand, scale their usage up or down as needed, and collaborate and share data with others.

In conclusion, cloud computing is based on the principles of software as a service mode and a common objective for all users. The SaaS model allows users to access and use software applications over the internet without the need for local installation or maintenance. The common objective of all users is to leverage the shared infrastructure and services provided by the cloud computing environment to access scalable, flexible, and cost-effective computing resources.

A