Basic General Knowledge
To produce sound it is necessary that

the source may execute any type of vibrations
the vibrations of source are not necessary
the source should execute longitudinal vibrations
the source should execute transverse vibrations

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Basic General Knowledge
Yuri Gagarin was

the first person to fly at great height of about 340 km from the earth
both (a) and (b)
None of these
a Russian cosmonaut & became the first man to travel in space.

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