山路时而平坦,时而陡峭,考验着骑行者的体力和耐心。Shānlù shí'ér píngtǎn, shí'ér dǒuqiào, kǎoyàn zhe qíxíngzhě de tǐlì hé nàixīn.The mountain road was sometimes flat and sometimes steep, testing the riders' strength and patience.
天气时而晴朗,时而下雨,让人难以安排行程。Tiānqì shí'ér qínglǎng, shí'ér xiàyǔ, ràng rén nányǐ ānpái xíngchéng.The weather was sometimes sunny and sometimes rainy, making it hard to plan a trip.
海面上时而传来几声海鸥的叫声。Hǎimiàn shàng shí'ér chuánlái jǐ shēng hǎi'ōu de jiàoshēng.Now and then a few calls of seagulls came over the sea.