完形填空

March 12 is Tree Planting Day．Do you know how 　　1　　 a tree．First, the 　　2　　 must be just right－neither too wet nor too 　　3　　．It’s best to plant trees in 　　4　　 because it’s 　　5　　．Dig a hole 　　6　　 for the tree．But the hole should not be 　　7　　 deep．Second, knock a long, strong stick into the earth 　　8　　 to the hole．　　9　　 sure that it is straight．Then put the tree in the hole 　　10　　 it is straight．　　11　　that, you should put the 　　12　　 back in the hole again, and 　　13　　 it down hard with your foot several times．Tie the tree 　　14　　 the top of the stick to keep it straight．As last you should water it well, as 　　15　　 as possible．