To make an electromagnet you need to send a current through the wire.为了做成电磁体你需要对金属线送电.The principle of electromagnet induction had thus been discovered.电磁感应定律就是这样发现的.Reset pneumatic spring, mechanical spring reset, reset...
...Roosevelt's immortal words, 'Speak softly and carry a big stick.'罗斯福的不朽名言——“说话温和,手持大棒”Roosevelt was elected four times to the presidency of the United States.罗斯福连续当选四届美国总统。The victory inspired him to di...