The statement acts like a chain of if statements. each performs its test, one after the other, until one of them is found to be true or until the construct is exited without any test ever evaluating to true.

if then elseif

Explanation:

It can be a chain of statement as shown below:

while(condition)

{

      if( condition){

       Then {

             }

          }

     else if {

      }

}

If...Then...ElseIf

Explanation:

If... Then... ElseIf statement perform their tests, one after the other, until one of them is found to be true.

system programmer option d is correct

because an operating system is software that manages computer hardware and system resources.