Chapter 1, Problem 29CP

Which of the following preprocessor directive is correct?

$\begin{array}{l}\text{a}\text{.}\text{import iostream}\\ \text{b}\text{.}\text{\#include}<\text{iostream}>\\ \text{c}\text{.}\text{include}<\text{iostream}>\\ \text{d}\text{.}\text{\#include iostream}\end{array}$