Scientists created ultra fine films of specialized crystals by means of ______.

A．The two strands making up DNA's double helix can find each other easily in a complex chemical mixture
B．Evolution has solved the problem of building a computer smaller than a speck of dust a long time before
C．DNA not only programs cells to replicate themselves but also instructs them how to assemble individual molecules into new materials
D．The read-head components for computer hard drives are constructed by means of the technology known as a molecular beam epitaxy

A．inopportune
B．importunate
C．incongruous
D．unfitting