Choose the pair of words that are always used in the singular form (सदा एकवचन).

Let's analyze the grammatical number usage of the terms in each option:
* वर्षा, जनता: Both words are always used in the singular form (सदा एकवचन). For example, "जनता आ रही है" or "वर्षा हो रही है".
* प्राण, बाल, होश, लोग, हस्ताक्षर: These words are always used in the plural form (सदा बहुवचन). For example, "उनके प्राण निकल गए", "बाल कट गए", "होश उड़ गए", "लोग कह रहे हैं", "हस्ताक्षर कर दिए".

Therefore, the pair that is always used in the singular form is वर्षा, जनता.