题目

The idea for a science experiment can come from an unusual place. After watching a YouTube video of a dancing bird named Snowball, a scientist in Californina decided to study the ability of animals to keep the beat. Bird lovers have long claimed that their pets have rhyhm, and there are many videos of dancing birds online. Until now, scientists have suspected that humans are the only animals that can accurately keep rhythm with music. Thanks to Snowball, that scientific opinion is changing. Snowball is a cockatoo, a kind of parrot, and his favorite song is “Everybody” by the Backstreet Boy 用“伏安法”测电阻的实验中，某同学连接了如图所示的电路，电路连接中存在几处错误和不足，请你找出来(待测电阻值约为15 Ω)． ①________； ②________； ③________．