Choose the word that best fits each gap.

Venus has been known (1) __________  prehistoric times.  It is the brightest object in the sky (2) __________  for the Sun and the Moon.  Like Mercury, it was popularly thought to be two separate bodies: Eosphorus as the morning star and Hesperus as the evening star, but the Greek astronomers (3) __________ better.

The first spacecraft to visit Venus was Mariner 2 in 1962. It has subsequently been visited by many others (more than twenty (4) __________), including Pioneer Venus and the Soviet Venera (5) __________ returned the first photographs of the surface.

1 a) since b) for c) during d) after

2 a) as b) except c) otherwise d) even

3 a) had known b) were knowing c) knew d) know

4 a) before b) until then c) by the time d) so far

5 a) who b) which c) whose d) what