Texting while walking is something that most of us are guilty of．We can't help ____(reply)to that message we just received．However，while it's fun to keep up to what's going on，we may actually put____(we)in danger．

    A team of researchers from UK recently found people____use their phones while on the move walk differently．During the research，a group of 21 volunteers____(ask)to walk around a street with obstacles(障碍物)such as a step.____volunteers traveled the course a total of 12 times each，either writing or reading a message，making a call，or with no phone at all．It took the volunteers 118 percent ____(long)to complete the course while using a phone．They also paid attention to the travel path 51 percent more when they weren't using a phone．“Although there____(be)no accidents，we should still be aware____what's going on around us，”according to Matthew Timmis，co—author of the study．The big risk is suddenly—appearing situations，like someone suddenly walking in front of you．You are not going to be able to respond to that____(swift)enough，so you may injure yourself or get injured．In a word，these hidden____ (danger)of texting while walking should be recognized to avoid injuries．

下列实验操作中，正确的是（　　）