Fill in the blanks with appropriate linkers given in brackets:
Aesop is afigure clouded in so much mystery and legend ......... it is difficult to know .......... can be said about him. It is also strange to believe ............. this world-famous man was born a **** in the sixth century B.C. ............ slaves were bought and sold frequently. Aesop’ Greek master gave him liberty .......... he was impressed by his learning and wit.
[because, that, what, when]