Which of the following is the definition of the entry cijc_{ij}cij of the product C=ABC = ABC=AB?
cij=∑k=1naikbkjc_{ij} = \sum_{k=1}^n a_{ik} b_{kj}cij=∑k=1naikbkj
cij=∑k=1nakjbikc_{ij} = \sum_{k=1}^n a_{kj} b_{ik}cij=∑k=1nakjbik
cij=∑k=1nakibjkc_{ij} = \sum_{k=1}^n a_{ki} b_{jk}cij=∑k=1nakibjk
cij=∑k=1naikbjkc_{ij} = \sum_{k=1}^n a_{ik} b_{jk}cij=∑k=1naikbjk