Answer:
4. Command line interface (CLI)
Explanation:
An operating system is a system software pre-installed on a computing device to manage or control software application, computer hardware and user processes.
This ultimately implies that, an operating system acts as an interface or intermediary between the computer end user and the hardware portion of the computer system (computer hardware) in the processing and execution of instructions.
Some examples of an operating system on computers are QNX, Linux, OpenVMS, MacOS, Microsoft windows, IBM, Solaris, VM etc.
A Command line interface (CLI) refers to a text-based user interface that allow users to operate a software application or program, as well as manage and execute operating system functions by typing standard line of commands into the text-based user interface with a real-time response.
Basically, the CLI is solely text-based and as such requires a thorough knowledge and understanding of global commands, as well as administrative privileges in some cases. 
<em>Hence, the operating system function which has a steeper learning curve (more difficult to learn) and can potentially break the system without careful use of its operations is the Command line interface (CLI). </em>
 
        
             
        
        
        
The command is Merge & Center
This command could be easily found in the toolbar of your excel.
If you execute this command in two different cells, those cells will be merged into one larger cell and the content in that cells will be placed exactly in the middle of the combined cell (measures according to combined cells' length)
        
             
        
        
        
Answer:
Time Complexity of Problem - O(n)
Explanation:
When n= 1024 time taken is t. on a particular computer.
When computer is 8 times faster in same time t , n can be equal to 8192. It means on increasing processing speed input grows linearly.
When computer is 8 times slow then with same time t , n will be 128 which is (1/8)th time 1024.
It means with increase in processing speed by x factor time taken will decrease by (1/x) factor. Or input size can be increased by x times. This signifies that time taken by program grows linearly with input size n. Therefore time complexity of problem will be O(n).
If we double the speed of original machine then we can solve problems of size 2n in time t.
 
        
             
        
        
        
A) IS MOSTLY JUST ENGINE Oil.