Use the model to add the fractions. (3 points) A fraction strip partitioned into seven parts with one part shaded. Another fraction strip partitioned into seven parts with one part shaded. An addition sign separates the two fraction strips. After second fraction strip there is an equal symbol and another fraction strip with seven parts with no parts shaded. Under the first fraction strip is the fraction one seventh. Under the second fraction strip is the fraction one seventh.
a

two sevenths
b

four sevenths
c

five sevenths
d

six sevenths