${?}_{{?}_{{?}_{?}}{?}_{{?}_{?}}{?}_{{?}_{?}}{?}_{{?}_{?}}{?}_r\text{e}\text{f}\text{e}\text{r}\text{s}to\text{p}\text{r}\text{a}\text{c}\text{t}\text{i}\text{c}\text{i}\text{n}\text{g}\text{a}\text{t}\text{a}\text{s}\text{k}\text{c}\text{o}\text{n}\text{t}\text{i}\text{n}\text{u}\text{o}\text{u}\text{s}\text{l}\text{y}\text{w}\text{i}\text{t}\text{h}\text{o}\text{u}\text{t}\text{b}\text{r}\text{e}\text{a}\text{k}\text{s}\text{.}}$

$a.$

Massed practice

$b.$

Whole practice

$c.$

Continuous learning

$d.$

Overlearning