21. –Jimmy had a lot of parties recently.

—Yes, that might      why he didn’t do well in the test.

A£®sum up    B£®add up to   C£®account for   D£®make sense of

22.A dictionary is necessary if you want to learn English, so you’d better buy    .

A£®this    B£®that    C£®it   D£®one

23.While she is a lovely girl, she    be extremely difficult to work with.

A£®may     B£®must    C£®should   D£®can