In scientific notation, the first part is always between 1 and 9, otherwise the exponent would change. So, for example, 10.1*10.^5 would not be correct, but could be written as 1.01*10^6. Likewise, .101*10^8 would not be correct, but it could be written as 1.01*10^7. So for this question, choice a is correct.
