Read the following statements regarding sexual reproduction and select the set of correct statements.

$\left(\mathrm{a.}\right)$ Sexual reproduction mostly involves two parents.
$\left(\mathrm{b.}\right)$ It generally involves gametic fusion.
$\left(\mathrm{c.}\right)$ Meiosis does not occur in sexual reproduction.
$\left(\mathrm{d.}\right)$ External fertilization is a characteristic of sexual reproduction.