In a Star topology, all the nodes (devices) are connected directly to a central server or hub. This central hub acts as a mediator to transmit data between devices. If one node wants to communicate with another, it must go through the central server or hub.

The User Interface (UI) is what controls the interaction between the user and the operating system. It allows users to interact with the system through visual elements (like windows, icons, and menus) or command-line instructions, enabling communication and efficient operation.

Page margins in MS-Word refer to the blank spaces around the edges of the page. The margins include the top, bottom, left, and right edges of the page. These settings determine the space between the text and the edge of the page.

• (a) Right: Right margin.
• (b) Left: Left margin.
• (d) Top: Top margin.

However, (c) Centre is not considered a part of the page margin. The center refers to the alignment of text within the page, not the page margins themselves.

Therefore, Centre is not part of the page margin.

Non-volatile storage refers to a type of memory that retains data even when the power is turned off. 

Secondary Storage: This is non-volatile storage, which includes devices like hard drives, SSDs, USB drives, and optical discs. It stores data permanently until deleted by the user.

Line spacing refers to the amount of vertical space between lines of text in a document. It determines how much space is placed above and below each line of text, improving readability and overall layout.