Which of the following identifies two technological advancements during the dawn of the space age between 1951 and 1959?
a. the first successful orbiting satellite was launched by the soviet union, and several space craft launches in the advancement of space exploration.
b. the first human was sent into space, and water was discovered on mars.
c. numerous spacecraft launches resulted in technological advancements, and humans landed on the moon.
d. robotic spacecrafts were sent to gather information about halley’s comet, and the twin voyagers gathered data from distant planets.

Letter A. The first successful orbital satellite was launched by the Soviet Union and several spacecraft launches helped advance space exploration.

Explanation:

Between 1951 and 1959, Sputnik 1 was the first artificial satellite on Earth. It was launched by the Soviet Union on October 4, 1957, at the Soviet Union Nebula Testing Unit currently known as the Baikonur Cosmodrome. In addition, there were other spacecraft launches that advanced space exploration, such as Sputnik 2, launched in space on November 3, conquering the feat of sending the first living creature into space, a dog named Laika.

a and b

substitution is the answer in this case