Activity in China’s manufacturing sector is expected to have contracted for a fifth straight month in December, a Reuters poll showed, likely consigning the world’s second-largest economy to its slowest annual growth in a quarter of a century. The official manufacturing Purchasing Managers’ Index (PMI) is forecast to inch up to 49.7 from November’s 49.6, according to a median forecast of 27 economists in a Reuters poll. Analysts expect only a marginal improvement in the vast manufacturing sector in December from November, when activity fell to a three-year low.