根据短文内容，选择最佳答案。
Emily
and Alex were happy when their family moved to a house with a very big garden. They
could climb up trees, grow flowers and even play badminton. They liked to watch
the birds flying among the trees in the garden. They even started to put food out
to attract（吸引）
more birds.
Everything
was fine for a few days until one afternoon there was a strange bumping noise on
a window. Emily went outside and found a small bird dead on the grass. Its neck
seemed to be broken.
"It
must have flown into the window," Alex said when his sister Emily called him
to have a look. "Ah, yes, look here. You can see the mark where it hit the
window. There are a couple of tiny feathers stuck(粘贴) on the window."
"Poor
thing!" Emily said.
During
the next month, another five birds died in the same way. "Why would they fly
to the windows?" they wondered. Finally they found out the truth. When the
birds were flying, they couldn't see into the rooms. All they saw was the reflection(反射) of the garden. They thought that they were flying into trees because
they saw trees reflected by the window.
"Something
has to be done to save the birds." the parents decided.
At first,
he family tried keeping curtains（窗帘）across the windows, but this
made the room dark. Then they bought some strong black paper and cut out the shape
of a hawk. They made six hawks—one for each window. They stuck the hawks to the windows. They looked
pretty and did not keep out much light. When the birds saw the hawks, they would
fly away.
After
that, there were no more dead birds. The family were much happier.
