16.Mr Russel is a good teacher, but he often gives ____ lectures.
A. excellent B. extensive C. sound D. tedious

<tedious>
tedious 很郁闷的、很惹人烦的、单调乏味的
</tedious>

<excellent>
excellent 优秀的、很好的
out-standing 最优秀、杰出的
</excellent>

<extensive>
extensive 广泛的、广大的
</extensive>

<sound>
sound n.声音、adj.非常好的、健全的
</sound>