题目

The term “telecommuting” refers to a workforce arrangement in which there is no central office where employees gather and work. Instead, these employees work wherever they can access the people and materials needed to complete their projects and daily tasks. One of the most common locations for telecommuters to work is their own homes. However, with today's advanced technological equipment, employees can work anywhere. Laptop computers and tablets allow for facile mobility, as do wireless Internet “hot spots” and even smartphones with highspeed Internet connectivity.More employers shou（2007•乌兰察布）考虑下面4个命题：①若一条直线上的两点到另一条直线的距离相等，则这两条直线平行；②有一个角是100°的两个等腰三角形相似；③对角线互相垂直且相等的四边形是正方形；④对角线相等的梯形是等腰梯形．其中正确命题的序号是    ．（把你认为是正确命题的序号都填上）