Final answer:
The greatest possible product of four different prime numbers each less than 20 is found by multiplying the four largest primes in that range: 19, 17, 13, and 11, which equals 46,189.
Step-by-step explanation:
To find the greatest possible product of four different prime numbers each less than 20, we should choose the four largest prime numbers in that range. The largest primes less than 20 are 19, 17, 13, and 11. Multiplying these together gives us:
19 \times 17 \times 13 \times 11 = 46,189.
Thus, the greatest possible result when multiplying four different prime numbers, each less than 20, is 46,189, which matches option 'd'.