Since computers were introduced, they____ to be useful tools for people weak in math.
A、had proved
B、have proved
C、 will prove
D、are proving
Directions:In each of the following groups of words, there are four underlined letters or ltter combinations marked A, B, C and D. Compare the underlined parts and identify the one that is different from the others in pronunciation. Mark your answer by blackening the corresponding letter on the Answer Sheet.