HPLC系统性试验 一般要求拖尾因子T应在0.95-1.05。
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___ pictures in the park last weekend.
A. take
B. took
C. was
D. draw
Did you ___football yesterday?
A. play
B. played
C. were
D. are
He always _____me last term.
A. helped
B. helps
C. helping
D. help
They came to China in 1990.(变一般疑问句)__________ they ________ to China in 1990?