Gas, water and electricity

In a suburb three new houses all have to be connected to a gas (red), water (blue) and electricity (green) supply. All houses should get their own gas, water and electricity connection. Furthermore no connections may cross each other. Because of the danger of stealing, no connections are laid below a house. In the figure on the right-hand side the situation is sketched. The red squares are the houses, the circles the point from which the connections should go to the houses. Why is it impossible to lay down all connections in such a way that no connection crosses another connection?

Horse inheritance

The last will of a horse breeder is that all his horses are to be given to his three children in the following ratio: 1/2:1/3:1/9. At the moment the horse breeder passed away he owned 17 horses. How could his last will be followed?

Jars

You've got two jars, one of them fits exactly 5 litres, the other one fits exactly 3 litres. How could you get exactly 4 litres with these two jars? It is allowed to spoil some water.