1 . 孩子们正在堆雪人，他们的手又红又冷。（with 复合结构）
The children were making a snowman, ________.

2 . Through intense effort，Yuan Longping o________（克服）enormous technical difficulties to develop the first hybrid rice. （根据中英文提示填空）

3 . These works of art really do ______ across the centuries as if time itself were nothing.
这些作品穿越几个世纪，出现在我们面前，仿佛时间没有流逝一般。