题目

A long time ago, my grandma and grandpa lived in a house with a big front yard. They planted lots of vegetables and flowers in the yard.They worked hard to keep the garden growing. All summer long, the family ate food from the garden and enjoyed the flowers.Years passed. It became harder for them to keep up the garden. So they made it a little smaller.Then one summer Grandpa died. It was a lonely winter for Grandma. It was hard for her to care for the garden alone. When spring came, she planted just a few vegetables and flowers.One day in the early summer, Grandma heard big noises in the yard.关于同步卫星是指相对于地面不动的人造卫星，有关说法正确的是（     ） ①同步卫星不绕地球运动         ②同步卫星绕地球运动的周期等于地球自转的周期③同步卫星只能在赤道的正上方   ④同步卫星可以在地面上任一点的正上方 ⑤同步卫星离地面的高度一定     ⑥同步卫星离地面的高度可按需要选择不同的数值A．①③⑤  　 B．②④⑥　    C．①④⑥　　　Ｄ．②③⑤