已知P是△ABC所在平面内一点，$\overrightarrow{PB}+\overrightarrow{PC}+2\overrightarrow{PA}=\overrightarrow{0}$，现将一粒红豆随机撒在△ABC内，则红豆落在△PBC内的概率是（      ）

    Currently offered by some famous universities, MOOCs are attractive to people who do not have the financial resources to meet the growing costs of university education, or who do not have formal qualifications. They also allow participants to study at their own pace.

    The potential for MOOCs to deliver education is obviously vast—they could be considered as a huge step forwards in widening participation. They also have the potential to provide a unique window on universities that offer popular and valuable courses, they may attract some participants to register for formal fee-paying programmes at the same or other universities and are likely to promote new ways of on-line education.

    However, it is still very early days for MOOCs. The quality of the education provision is highly variable, with many courses offering only recordings of lectures, and delivery is particularly difficult in some special fields that require practical classes, research projects or extensive library access. Besides, wider engagement with participants requires very considerable resource. Even limited feedback or examination becomes a major task if there are several thousand students in the class.

Considering the challenges, some people argue MOOCs will soon evaporate (蒸发). But they certainly provide good opportunity for widening higher education, are a means of raising awareness of universities to audiences of tens or hundreds of thousands, and are well worthy of serious consideration.

How to Protect Your Ears

    You and your friends are leaving a concert on a Friday night. When you get outside, your ears are ringing. You have to shout to be heard. ____ So no harm done…right?

    Not quite. Temporary buzzing may be easy to ignore, but repeated exposure to loud noise will eventually cause serious— and irreversible(无法治愈的)—hearing loss. A new study conducted by researchers at Brigham and Women's Hospital in Boston shows that one in five people between the ages of 12 and 19 are experiencing slight hearing loss, and one in 20 have mild hearing loss. ____

    But the good news is that there plenty of ways you can protect your ears from further damage — and still listen to the music you love:

    Ask around. Put your earbuds in or your headphones on, and then ask a friend next to you whether or not he or she can hear what you're listening to. ____ Turn it down.

    Buy noise-canceling headphones. A pair of earbuds or headphones that fits comfortably will limit outside noise so that you can hear your music better at lower volumes.

    Take breaks. ____ So when listening to music, take your headphones off for 15 or 20 minutes and let your ears enjoy the quiet.

    ____ You can buy a cheap pair at any drugstore as an easy way to lower volume at concerts — or while playing or practicing your own music — without changing the quality of the sound.

A. Use earplugs.

B. Keep the volume below 70 percent.

C. If the answer is yes, your music is too loud.

D. Like every other part of your body, your ears need rest.

E. But by morning, your hearing is totally back to normal.

F. Unfortunately, there's no way to get back hearing you've already lost.

G. The exposure to noise is louder and longer than in any previous generation.