How long ________ they ________ (dig) the ditch?
have … been digging
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I prefer this diagram ________ that one.
Those who’d like to visit the exhibition ________ (sign) your names here.
Ihavebeenstudyinghereforfouryears,bynextsummerI________.
Thistest________anumberofmultiplechoicequestions.
Somemoleculesarelargeenough________(see)undertheelectronicmicroscope.