--What do you think of cloning?

--No doubt it’s a great invention. But ________, it may have some side effects.

A．if not properly handling

B．if properly not handled

C．if not properly handled

D．if properly not handling

用一根细线系住一块石块，用手提住线把石块浸到水中．在石块从接触水面到全浸入水的过程中，石块受到的浮力是______的（填变化情况）．当石块全浸在水中时，石块受到的浮力为F₁，松开线让石块沉到水底，石块受到的浮力为F₂，则F₁______F₂．