A teacher spot-checks how students are doing by walking around the room, selecting students to observe at random and then reinforcing those who are working well. What type of schedule is being used?

Variable interval

Explanation:

In operant conditioning, a variable-interval schedule is a schedule of reinforcement where a response is rewarded after an unpredictable amount of time has passed, which is the opposite of a fixed-interval schedule. This schedule produces a slow, steady rate of response.

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.

d.

thist title points out that you are explaining the nature of the u.s. government. it is the most specific. a representative government consists of a government where decisions are taken according to a voting system. the most essential aspect of a representative government is found in the different structures where voting rights are granted to different groups of people. for example, voting for governor, mayor, president, local police chief etc.