Final answer:
The two metalloids that act both as metals and non-metals are boron and silicon, known for their semiconductor properties and their important role in electronics.
Step-by-step explanation:
The two metalloids that characteristicly behave as both metals and non-metals are boron and silicon. These metalloids exhibit intermediate properties between that of metals and nonmetals. For instance, they both form covalent crystals as nonmetals do, but do not generally form monatomic anions like metals. A notable property of boron is its semiconducting nature, while silicon is extensively used in electronics precisely because it is a semiconductor. Semiconductors are special because their conductivity increases with temperature, unlike typical metallic conductors.
Regarding the options provided in the question, option A, Silicon and Boron have high melting points, is not accurate in describing the 'catch' to their metalloid behavior. Rather, their characteristic as semiconductors and their variable conductivity with temperature is more significant.