Substances that conduct an electric current only under certain conditions are most likely to be .
Question options:

metals

nonmetals

metalloids

noble gases

Substances that conduct an electric current only under certain conditions are most likely to be METALLOIDS

Explanation:

Metalloids conducts electricity and allows the passage of electron which enhances their conductivity and make them suitable for it. Although this ability is only achieved when there is an increase in temperature in order to achieve this feat.

1. (1.2kw)x(15/60hours) = .3kwh --> a

2. (5kw)x(90/60hours)x(8cents/kwh) = $0.60 --> d

3. microwave --> 1200 watts = (1.2kw)x(6/60hours) = .12kwh

coffee-maker --> 900 watts = (.9kw)x(10/60hours) = .15kwh

therefore, it requires more energy for the coffee-maker to do the same amount of work.

so the answer is a.