根据短文内容回答下列问题。

    In the UK, bus journeys are very common. Buses are often convenient(便利的) for the people who live or work in the city centre. Passengers can avoid heavy traffic and do not have to pay for the parking. However, taking the bus is just a necessary but boring part of life: They get on the bus, pay for it and sit down or find a place to stand when it is crowded. Everyone seems sad and bored.

    In Latin America, however, bus trips can be wonderful. For a start, films are showed on the buses between cities for passengers to have fun along the journeys. Local buses do not show films, but drivers usually turn on the radio and it can be great for passengers to listen to songs and get relaxed.

    Even better than films and music are the sights and sounds on the buses. Local buses always go to parts of the town that passengers would not visit by themselves. There passengers can see shops that they have never heard about. And they can also see other cultures of the town from the windows of the buses.

    Besides, passengers' luggage(行李) is also interesting. It is common to see a happy dog's head getting out of somebody's bag or a lovely chicken "speaking cheerfully" under somebody's arm. Once on a bus in Peru, a farmer even tied a sheep to the top of the bus. It was quite surprising.

    In all, taking the bus in Latin America is really fun and unforgettable.

（I）当x＞0时，求函数g（x）=f（x）+ln（x+1）+ $\frac{1}{2}$ x的单调区间；

（Ⅱ）当a∈Z时，若存在x≥0，使不等式f（x）＜0成立，求a的最小值．