In a plant physiology experiment a green plant kept in light was found releasing more units of $^{18}O_2$. Which of the following compounds would have been supplied to that plant ?

Question

$\begin {array} {1 1} (1)\;C_6H_{12}O_6\: containing\: ^{18}O & \quad (2)\;CO_2\: containing \: ^{18}O \\ (3)\;Ozone\: containing\: ^{18}O & \quad (4)\;H_2O\: containing ^{18}O \end {array}$