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【简答题】
x<-data.frame(val=c(5,2,1,3,4,6)),采用which()函数返回值为偶数的行的索引,可写做:_____________ (注:字符之间不留空格)
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举一反三
【单选题】The use of an anchor to assist in turning in restricted waters is _____.
A.
the sign of a novice ship-handler
B.
to be used only with a single-screw vessel
C.
good seamanship
D.
a last resort
【简答题】国内最早提出“教育形成交往起源说”的人是（ ）。
【简答题】本子套题——商品编辑——主辅图
【单选题】A vessel using a traffic separation scheme shall（）.
A.
only anchor in the separation zone
B.
avoid crossing traffic lanes，but if obliged to do so，shall cross on a heading at as small an angle as is practical
C.
avoid anchoring in areas near the termination of the scheme
D.
use the separation zone for navigation through the scheme if she is hindering other traffic due to her slower speed
【单选题】You are planning to anchor in an area where several anchors have been lost due to fouling．As a precaution，you should ______．
A.
anchor using both anchors
B.
anchor with scope of 8 or more to 1
C.
use a stern anchor
D.
fit a crown strap and work wire to the anchor
【单选题】You are planning to anchor in an area where several anchors have been lost due to fouling. As a precaution, you should ______.
A.
anchor using both anchors
B.
anchor with scope of 8 or more to 1
C.
use a stem anchor
D.
fit a crown strap and work wire to the anchor
【简答题】国内最早提出“教育形成交往起源说”的人是（ ）。
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