题目

How was 2019 for you? Was it pleasant and full of joy? Or was it unpleasant and full of sadness? Either way, some good things happened this year that can warm your heart. Let's take a look.A Thailand supermarket came up with a great way to cut down the plastic packaging. It wraps the things in banana leaves instead of plastic.South Korea is having the daytime disco parties for people over 65.The goal is to help fight loneliness and dementia in the elderly people.There are only two northern white rhinos left in the world. They live in Africa. This year, scientists successfully fertilized seven 1．若0＜α＜$\frac{π}{2}$，-$\frac{π}{2}$＜β＜0，cos（α+$\frac{π}{4}$）=$\frac{1}{3}$，sin（$\frac{π}{4}$-$\frac{β}{2}$）=$\frac{{\sqrt{3}}}{3}$，则cos（α+$\frac{β}{2}$）=（　　）A．$\frac{{\sqrt{3}}}{3}$B．$-\frac{{\sqrt{3}}}{3}$C．$\frac{{\sqrt{6}}}{3}$D．$-\frac{{\sqrt{6}}}{9}$