Final answer:
To obtain the best spatial resolution, one should select the smallest cassette size which is the 18cm x 24cm (8x10) option.
Step-by-step explanation:
To select a cassette to produce an image with the best spatial resolution, one would typically choose the smallest size because the image receptor's pixel size will be smaller, thus providing better detail in the image produced. In this scenario, the best choice for the highest spatial resolution is:
A. 18cm x 24cm (8x10)
The smaller the film or digital sensor, the less distance there is for the light to spread, which generally results in a sharper image with more detail. The cassette that corresponds to 18cm x 24cm (8x10) will produce images with finer spatial resolution compared to the other options.