The proposal to lay a telegraph cable from Europe to America made oceanographic studies take on ______.

A．the American Navy
B．some early intercontinental travelers
C．those who earned a living from the sea
D．the company which proposed to lay an undersea cable

A．limited exposure to them does little harm to people's health
B．the present is more important for them than the future
C．the danger does not become apparent immediately
D．humans are capable of withstanding small amounts of poisoning