A factory has 157 managerial, 52 inspection, 1473 production and 215 office-work employees. A person is chosen at random. The probability that he is involved in management duty is —

• a$\frac{157}{1897}$
• b$\frac{52}{1897}$
• c$\frac{1473}{1897}$
• d$\frac{215}{1897}$