单项选择题

I was not at all happy at the prospect of the 700-mile drive from Dar es Salaam to Nairobi. It was not that I disliked driving but I suspected that what is a very pleasant trip in the dry season could prove disastrous during the long rains, and the monsoons had arrived the previous week. I was fully aware of the possibility of a breakdown, of hitting large animals as they stopped, dazzled by my headlamps, or even of skidding off the road. But these dangers worried me much less than the thought of the stretches of black cotton soil I would have to negotiate, gray and hard as concrete when dry, but a black, viscous, muddy mess with the consistency of elastic after just one heavy shower of rain. However, I had to be in Nairobi by the weekend so there was nothing for it but to drive; all planes were fully booked three weeks ahead and with the railway line washed out there was little likelihood of a train in the next few days.
　　The first half of the journey proved completely uneventful, and I was in a very cheerful frame of mind as I pulled in to Moshi in the misty dawn. A little later, buoyed up by an excellent breakfast and the thought of tarmac roads all the way to the border, I resumed my journey. I drove another 80 miles; I was now within 20 miles of the border and what I saw ahead matched my spirits. Gone were the hills, completely hidden by the lowering clouds, their ominous, gloomy depths rent by jagged flashes of lightning.
　　Ten minutes later the rain struck--an almost solid wall of water that smashed down on the car in a noisy frenzy, sheeted down the windscreen and made it almost impossible for me to see where I was going. The windscreen wipers did little to help; they were not designed to cope with such an avalanche of water. But rain of such intensity could not last long, and by the time I reached the border check-point the rain had eased off to proportions I felt I could cope with.
　　The check-point consisted of two poles resting on tar barrels with the half-completed structure of a modem control post in between. In six months or so, everything would be complete as far as I could see. In the meantime, the officials I needed to stamp my passport and check my luggage could only be in the bedraggled tent I noticed perched on a slope over to my left. I took off my shoes and socks, climbed out of my car and dashed over to the tent. In the tent was an impeccably dressed immigration official sitting on a chair with his feet tucked under him while a river of water flowed in under one wall of the tent and out under another. These were hardly ideal working conditions. Yet nobody would have thought that, as he saw me, he could grin cheerfully and extend a very courteous welcome.
It can be inferred that the writer might be ______ when the immigration official grinned cheerfully to him.