${?}_{{?}_{{?}_{?}}{?}_{i}s\text{t}\text{h}\text{e}\text{f}\text{i}\text{r}\text{s}\text{t}\text{c}\text{o}\text{n}\text{d}\text{i}\text{t}\text{i}\text{o}\text{n}\text{t}\text{h}\text{a}\text{t}\text{m}\text{u}\text{s}\text{t}be\text{m}\text{e}\text{t}to\text{c}\text{r}\text{e}\text{a}\text{t}\text{e}\text{a}\text{p}\text{r}\text{o}\text{d}\text{u}\text{c}\text{t}or\text{s}\text{e}\text{r}\text{v}\text{i}\text{c}\text{e}\text{b}\text{r}\text{a}\text{n}\text{d}\text{.}}$

$a.$

Relevance

$b.$

Perceived value

$c.$

Permission marketing

$d.$

Product differentiation