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As in Colorado, opponents have mounted a vigorous ad campaign, with teachers unions spending more than $4 million as of mid-October.

The question has cropped up in the race for governor, with all three candidates saying it goes too far. Republican Charles Baker and independent Timothy Cahill say they support returning the sales-tax rate to its previous level of 5 percent. Incumbent Democratic Gov. Deval Patrick said he also supports lowering the rate to 5 percent, when the state can afford it.

A brief look at some other noteworthy ballot items:

California’s Proposition 23 would suspend the state’s landmark greenhouse-gas emissions law until the unemployment rate falls to 5.5 percent for a year. It is backed by out-of-state oil companies; foes include outgoing GOP Gov. Arnold Schwarzenegger and alternative-energy entrepreneurs.

Measures in Oklahoma would declare English the state’s “common and unifying language” and prohibit state courts from considering international law or Islamic law, known as shariah, when deciding cases.

In the nation’s smallest state, a measure would shorten its formal name to Rhode Island instead of “Rhode Island and Providence Plantations.”