Final answer:
A b. layered structure suggests that a rock sample is sedimentary, as beds and laminations are typical features of sedimentary rocks.
Step-by-step explanation:
The observation that suggests a rock sample is sedimentary is a b. layered structure. In sedimentary rocks, layering or stratification is a key feature, which includes beds thicker than 1 cm and finer laminations for layers thinner than 1 cm.
Sedimentary rocks often display sedimentary structures such as cross-bedding, ripple marks, and mud cracks. These are observed in outcrops rather than hand samples and can show the direction of sediment transport.