Yesterday he bought a dictionary. It c_____ him 50 yuan.

问题描述:

Yesterday he bought a dictionary. It c_____ him 50 yuan.
到底应该填cost(过去式)还是costs(单三式)呢?
不是说客观事实用一般现在时吗?

这又不是客观事实,如The earth is round 这是客观事实
yesterday 为过去式,cost过去式为cost