Which happened earlier: Sputnik 1 launched or Explorer 1 launched?

Question 1

Which happened earlier?

A Sputnik 1 launched ✓ Earlier

B Explorer 1 launched

Sputnik 1 launched (4 October 1957) came before Explorer 1 launched (31 January 1958)

Question 2

Which happened earlier?

A Mariner 2 reaches Venus

B Vostok 1 launches Yuri Gagarin ✓ Earlier

Vostok 1 launches Yuri Gagarin (12 April 1961) came before Mariner 2 reaches Venus (14 December 1962)

Question 3

Which happened earlier?

A Hubble Space Telescope launched

B Voyager 1 launched ✓ Earlier

Voyager 1 launched (5 September 1977) came before Hubble Space Telescope launched (24 April 1990)

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