由¹H、²H、³H和¹⁶O、¹⁷O、¹⁸O可形成的水分子有（　　）

A．3种

B．6种

C．9种

D．18种

____ you eat the correct foods _____ be able to keep fit and stay healthy. [ ]

A. Only if ; will you

B. Only if ; you will

C. Unless ; will you

D. Unless ; you will