问题
选择题
Nothing but some ancient Chinese coins _______ in the sunken ship since they began the exploration.
A．were found
B．was found
C．have been found
D．has been found
答案
答案：D
考查时态。句意：自从他们探险以来，仅仅一些古代中国的货币在下沉的船中被找到了。题中含有自从他们探险到现在为止，动作持续到现在，所以选D。
L。已知两落地点在同一水平面上，该星球的半径为R，万有引力常量为G，求该星球的质量M。