There are specific types of systems analysts, such as...

Easy, guys.

When the text says: " The main responsibility of a systems analyst is to make certain the computer system of his or her employer is functioning efficiently.", it means that the systems analyst must work in his enterprise searching the best way for the computer system utilized in it, as we can see in "functioning efficiently''. That gives an ideia of a system working better than the others.

That was easy.

d-

A systems analyst generally works in the computer department of a company providing the research and information necessary to maintain an up-to-date computer system. The remainder of the options either extrapolates information from the text or gives it a slightly different spin from its intended meaning. For instance, "must work in the computer department" is too huge a constraint on the original passage,which states that as a rule of thumb the bulk of their work is in the quoted sector. 

Palavras-chave do texto para questão: update, providing the research, up-to-date. A 'c': must work in the computer department. é invalidada porque o texto afirma "but a systems analyst generally works in the computer department". Must implica obrigatoriedade, se em vez de "generally" fosse "always", aí sim estaria correto.

(D)

The main responsibility of a systems analyst is to make certain the computer system of his or her employer is functioning efficiently. To do this, a systems analyst may examine both the hardware and software currently being used and suggest or even design new programs to better meet the organization’s needs.

Tradução-->A principal responsabilidade de um analista de sistemas é garantir que o sistema do computador de seu empregador esteja funcionando de maneira eficiente. Para fazer isso, um analista de sistemas pode examinar o hardware e o software atualmente em uso e sugerir ou mesmo projetar novos programas para melhor atender às necessidades da organização.