—Oh, doctor, The wound on my leg is infected.  —You really shouldn’t have left it _______ to the sun. 

_______ people in the world are sending information by e-mail every day.

The committee accepted his proposal that a conference be held _______ to deal with the issues arising in the course.

I like taking risks, too. I suppose it ______ in the family.

(2013·江西，23)________ can be good at something for 40 years if he doesn't love it.