读“全国农民家庭人均纯收入抽样统计曲线图”，从图上看出，全国农民家庭人均纯收入(抽样份数：18529户)从1978年到1982年呈现上升趋势，出现这种趋势的主要原因是（   ）

Dear Liza,

    I will be ten years old on Friday, 22nd July. To celebrate my birthday, I will invite several friends and I hope that all of you will be able to come to the party on that day.

    There will be two parts in my party. The first will be at the swimming pool near our school. Please bring your swimsuit (游泳衣) and a change of clothes. We have planned some pool games. My parents will be at the pool to protect the swimmers. The pool party will be from 2 to 3 p.m.

    The second part of the party will be at my house. A bus will take us all from the pool to my house. A singer is coming to my house. He will sing popular songs for us. I am sure you will enjoy them. The home party may last till 5 p.m.

    Please let me know by Friday, 15th July, whether you will come to my party, so that I will know how much food to prepare.

Love

Tracy

①我国充分利用国际市场

②我国积极利用外资发展经济

③对外贸易成为我国经济发展的方向

④我国出口产品竞争力有所增强

下列说法正确的是（  ）