Final answer:
In yellow light, a blue sweater will appear (2) black because it cannot reflect the yellow light and will absorb it instead.
Step-by-step explanation:
The perception of color depends on the wavelengths of light that an object reflects into our eyes. A blue sweater appears blue because it reflects blue light and absorbs other colors. In the presence of only yellow light, the blue sweater will not reflect light since blue materials typically absorb wavelengths other than blue.
Therefore, the blue sweater will appear black because it is not reflecting the yellow light that is shining on it.