21. Which of the followings is not a proper means to maintain a proper look-out?
(A) By sight.
(B) By hearing.
(C) By echo sounder.
(D) By radar.

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統計： A(37), B(88), C(476), D(51), E(0) #2523271

詳解 (共 1 筆)

#5126749
題目意思是 以下哪一項不是保持適當瞭望...
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