Random assignment of participants is used exclusively in the _____ method

Which statement is the most descriptive shorthand term for the trade-off involved in "delay of gratification" research?

a. "Now versus tomorrow" b. "Nature versus culture" c. "Stop versus go" d. "Self versus society"

Which term describes a developing organism between 8 and approximately 40 weeks following conception in humans??

a. ?zygote b. ?ovum c. ?embryo d. ?fetus