To find out how much Cathy has read, we need to add up the fractions of the book that she read on Monday and Tuesday.
On Monday, she read start fraction 1 over 6 end fraction of the book.
On Tuesday, she read start fraction 2 over 6 end fraction of the book.
To add these fractions, we need to have a common denominator. The least common denominator for 6 and 6 is 6.
So, let's convert both fractions to have a denominator of 6:
On Monday, start fraction 1 over 6 end fraction is equivalent to start fraction 1 over 6 end fraction multiplied by start fraction 6 over 6 end fraction, which gives us start fraction 6 over 36 end fraction.
On Tuesday, start fraction 2 over 6 end fraction is equivalent to start fraction 2 over 6 end fraction multiplied by start fraction 6 over 6 end fraction, which gives us start fraction 12 over 36 end fraction.
Now, we can add the fractions:
start fraction 6 over 36 end fraction + start fraction 12 over 36 end fraction = start fraction 18 over 36 end fraction.
This fraction can be simplified to start fraction 1 over 2 end fraction.
So, Cathy has read one-half of the book.
The answer is (D) one-half.