Direction: In the following passage, some of the words have been left out. First read the passage over and try to understand what it is about. Then fill in the blanks with the help of the alternatives given.

The Solar System has been a complicated wonder for the astronomers. This is a (236) to which we may never have the exact answer. Man has wondered (237) the age of the Earth (238) ancient times. There were all kinds of (239) that seemed to have the (240). But man could not begin to (241) about the question scientifically until about 400 years (242), when it was proved that the (243) revolved round the Sun and the Earth was a (244) of our Solar System, then scientists knew where to (245).