Scientific models . a.
are based on a set of observations
b.
are used to replace experiments
c.
allow the study of existing systems only
d.
are rarely used

The soviet union beat the us to the first successful launch, with the october 4, 1957, orbiting of sputnik 1, and later beat the us to have the first human in earth orbit, yuri gagarin, on april 12, 1961. the "race" peaked with the july 20, 1969, us landing of the first humans on the moon with apollo 11