A mad scientist develops a new memory pill and wishes to test it on a group of 11th grade students. He has a large number of sugar pills manufactured that look and taste exactly like the memory pills. He asks the manufacturer to prepare 50 envelopes, each containing a month's worth of doses of the memory pills, and 50 more envelopes with the same doses of sugar pills.
The manufacturer then randomly labels the 100 envelopes with numbers from 00 to 99 and delivers them to the scientist. It has recorded which numbers go with the real pills, but it doesn't tell him. Which of the following adjectives describes this experiment?
A. Double-blind
B. Explanatory
C. Hawthorne
D. Blocked
E. Multi-factor