l like seeing kids happy and if they --- it makes my job a lot easiera\ areb\ doc\ haved\ will请说明理由好吗?

l like seeing kids happy and if they --- it makes my job a lot easier
a\ are
b\ do
c\ have
d\ will
请说明理由好吗?

A
表示they are happy
这是用来指代上文中的.