Many drivers dream of the day when they can sit back while their car drives itself．While several companies are working hard to make （33）___ a reality，self-driving cars still face many problems．

Google was one of the first （34）___ （get） into this industry．It （35）___ （develop） self-driving cars since 2009，and its new driverless car is called Firely．

But the driverless car is only a"fair weather friend"，the Daily Mail commented．

According to the MIT Technology Review，the current driverless cars can't react like a human driver．They can't drive in heavy rain or snow．

Chris Urmson，director of the Google car team，said that this is because the detection technology is not yet good enough to separate certain objects from weather conditions．In the cars'eyes，raindrops and snowflakes are the same as rocks，and cars stop for them．But if the manhole（下水道入口）ahead is left （36）___ （uncover），they drive over it without hesitation．

（37）___ all these problems，Urmson said driverless cars will happen more quickly than people think．

But even at that time，driverless cars won't be truly"driverless．"

In the US，only when someone sits in the driver's seat （38）___ driverless cars allowed on roads in certain states

European countries，Mexico，Chile，Brazil and Russian follow the United Nations Convention on Road Traffic．The convention used to say："Every driver （39）___ at all times be able to control his vehicle or to guide his animals．"A change was agreed in May，allowing a car to drive itself （40）___ a driver is in the car and able to take the wheel at any time．