Which quality helps self-employed graphic designers sell their work to clients?

Marketing knowledge.

Explanation:

Marketing traditionally refers to all activities that a company performs to promote the sale of products or services. Traditionally, marketing has been seen as the totality of all activities aimed at promoting the exchange of products or services together with the sales department.  

Today, in most developed economies, consumer needs play a more important role than the presence of surplus supply. Marketing has thus become a pre-eminent discipline in which identifying needs has become central. Therefore, all professionals who want to maximize their sales should have knowledge of this discipline, in order to cover most of their clients' needs.

your answer would be d.)

i've never seen you when you're smiling

it really gets under my skin

you say it's easy when it's faster

i still can't guess what you're after

it's the colour of your skin

your skin is black metallic

it's the colour of your skin

your skin is black metallic

your skin is black metallic

your skin is black metallic

i think of you when you're sleeping

of all the secrets that you're keeping

you can't stay all day under the covers

'cause under there you'll discover

it's the colour of your skin

your skin is black metallic

it's the colour of your skin

your skin is black metallic

your skin is black metallic

you're turning black

it's the colour of your skin

it's the colour of your

your skin is black metallic

your skin is black metallic

your skin is black metallic

you're turning black metallic

it's the colour of your skin

your skin is black metallic

your skin is black metallic

your skin is black metallic

your skin is black metallic

your skin is black metallic

your skin is black metallic