Two blonde girls were working for the city public works department. 
 
One would dig a hole and the other would follow behind her and fill the
 hole in. 
 
They worked up one side of the street, then down the other, then moved on
 to the next street, working furiously all day without rest, one girl
 digging a hole, the other girl filling it in again.
 
An onlooker was amazed at their hard work, but couldn't understand what
 they were doing. So he asked the hole digger, 'I'm impressed by the effort
 you two are putting in to your work, but I don't get it. 
 
Why do you dig a hole, only to have your partner follow behind and fill it
 up again? '
 
The hole digger wiped her brow and sighed, 'Well, I suppose it probably
 looks odd because we're normally a three-person team.
 
But today the girl who plants the trees called in sick..'