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【单选题】
在 HTML5 中,哪个属性用于规定输入字段是必填的? ( )A.
readonly
B.
required
C.
validat
D.
placeholder
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举一反三
【单选题】Many early Chinese immigrants worked in the mining industry, especially in the .
A.
copper mines
B.
silver mines
C.
coal mines
D.
gold mines
【简答题】MCS-51单片机正常工作所必须的外部硬件电路是_________、__________、________。
【单选题】听力原文：M: In the early 1860's many more Chinese arrived in California. Was there any improvement for Chinese's living conditions? F: Oh, no. This time the men were imported as work crews to construct th...
A.
in the early 1850's.
B.
in the late 1850's
C.
in the early1860's.
D.
in the late 1860's.
【单选题】Many early Chinese immigrants worked in the mining industry, especially in the _____.
A.
gold mines
B.
silver mines
C.
coal mines
D.
copper mines
【简答题】MCS-51单片机正常工作所必须的外部硬件电路是________、________、________。
【单选题】In the early 1860's many Chinese work crews were imported to ______.
A.
be railway builders
B.
be miners
C.
do the laundry
D.
run restaurants
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