( )all morning doing the experiment in the lab, John took a short lunch break.
A.正确答案BTo have spent
B.Having spent
C.Spending
D.Spend
( )all morning doing the experiment in the lab, John took a short lunch break.
( )all morning doing the experiment in the lab, John took a short lunch break.
A.正确答案BTo have spent
B.Having spent
C.Spending
D.Spend