放大摄影X线管焦点为0.05,允许的最大放大率为()
A.3倍
B.4倍
C.5倍
D.6倍
E.7倍
参考答案:C
People from all over the world make friends_____66____writing letters. One way to find a pen friend is to _____67____a club. International Pen Friends started in 1967 and has over 300,000members(成员) in different countries. Their____68___member is eight years old, and their oldest member is over 80. Some people write to find out about life in another country, ___69___want to practice their English, or enjoy their hobbies. Stamp collectors, for example, write to people in different countries ___70__that they can collect the stamps on the letters they receive. Most people just enjoy making friends, and they invite their pen friends to visit them.
在受到精神打击时,()会下降