两个共点力的大小都是50N,要使它们的合力也为50N,则这两个力的夹角为[ ]
A.30°
B.45°
C.60°
D.120°
答案:D
Electronic mail has become an extremely important and popular means of communication.The convenience and efficiency of electronic mail are threatened by the extremely rapid growth in the volume of unsolicited commercial electronic mail. Unsolicited commercial electronic mail is currently estimated to account for over half of all electronic mail traffic, up from an estimated 7 percent in 2001, and the volume continues to rise. Most of these messages are fraudulent or deceptive in one or more respects.The receipt of unsolicited commercial electronic mail may result in costs to recipients who cannot refuse to accept such mail and who incur costs for the storage of such mail, or for the time spent accessing, reviewing, and discarding such mail, or for both. The receipt of a large number of unwanted messages also decreases the convenience of electronic mail and creates a risk that wanted electronic mail messages, both commercial and noncommercial, will be lost, overlooked, or discarded amidst the larger volume of unwanted messages, thus reducing the reliability and usefulness of electronic mail to the recipient. Some commercial electronic mail contains material that many recipients may consider vulgar or pornographic in nature.The growth in unsolicited commercial electronic mail imposes significant monetary costs on providers of Internet access services, businesses, and educational and nonprofit institutions that carry and receive such mail, as there is a finite volume of mail that such providers, businesses, and institutions can handle without further investment in infrastructure. Many senders of unsolicited commercial electronic mail purposefully disguise the source of such mail.Many senders of unsolicited commercial electronic mail purposefully include misleading information in the messages’ subject lines in order to induce the recipients to view the messages. While some senders of commercial electronic mail messages provide simple and reliable ways for recipients to reject (or "opt-out" of) receipt of commercial electronic mail from such senders in the future, other senders provide no such "opt-out" mechanism, or refuse to honor the requests of recipients not to receive electronic mail from such senders in the future, or both.Many senders of bulk unsolicited commercial electronic mail use computer programs to gather large numbers of electronic mail addresses on an automated basis from Internet websites or online services where users must post their addresses in order to make full use of the website or service.The problems associated with the rapid growth and abuse of unsolicited commercial electronic mail cannot be solved by the government alone. The development and adoption of technological approaches and the pursuit of cooperative efforts with other countries will be necessary as well.
The word "induce" in Paragraph 5 is closest in meaning to ______.
A.cheat
B.introduce
C.provide
D.harm
关于慢性中耳炎与胆脂瘤,错误的是()
A.胆脂瘤可分为先天性和获得性两类
B.慢性化脓性乳突中耳炎的X线表现因其病变程度和乳突类型而不同,可分为单纯型、肉芽肿型和胆脂瘤型之多
C.胆脂瘤的个别病例为先天性肿瘤,无中耳感染病史
D.先天性胆脂瘤为位于完整鼓膜后的软组织肿物
E.胆脂瘤中的胶原酶或者其他异种炎症过程中引起骨质破坏