同位素示踪法可用于反应机理的研究，下列反应中同位素示踪表示正确的是（ ）
| A．2KMnO4 + 5H218O2 + 3H2SO4 ＝ K2SO4 + 2MnSO4 + 518O2↑ + 8H2O |
| B．2Na218O2 + 2H2O ＝ 4Na18OH + O2↑ |
C．NH4Cl + 2H2O NH3·2H2O + HCl |
| D．K37ClO3 + 6HCl ＝ K37Cl + 3Cl2 ↑+ 3H2O |
All the dishes in this menu, ______ otherwise stated, will serve two to three people. 
| A．as | B．if | C．though | D．unless |
The children loved their day trip, and they enjoyed the horse ride ______.
| A．most | B．more | C．less | D．little |
Progress______ so far very good and we are sure that the work will be finished on time.
| A．was | B．had been | C．has been | D．will be |
Charles was alone at home, with_______ looking after him.
| A．someone | B．anyone | C．not one | D．no one |
It is often ______ that human beings are naturally equipped to speak.
| A．said | B．to say | C．saying | D．being said |