Answers (a) and (c) have 3o
or 4o between temperature and dew point and the trend is
NOSIG. Answer (d) has the visibility temporarily reducing to
1,500m but returning to 4,000m. The remaining answer shows only one
degree between temperature and dew point and the visibility falling from 6,000m
to 1,600m in mist; it is likely to thicken to fog through the night.