Which scientific design has both practical limitations and limitations due to scale?

a. studying the effect of bleach on the growth of mold spores
b. exposing cultures of duckweed to different intensities of light
c. observing the replication of dna molecules with a hand lens
d. using colored marbles to model a cross between two colors of rabbits

C.observing the replication of DNA molecules with a hand lens

A scientific design is a framework which includes methodology and scientific protocol to derive a conclusion or result related to a scientific problem. Observing the replication of DNA molecules with a hand lens is a practical limitation and limitation due to scale. It is a practical limitation in a sense that replication which a biological process occurring in a cell cannot be observed by a simple hand lens. Limitation due to scale is because process of replication cannot be measured. Hand lens cannot be used for observing the process of replication, therefore, it is a limitation in methodology.