题目

It's nearly 7 o'clock. Jack ____________ be here at any moment. A . shall B . had to C . ought to D . have to 答案：C6．关于青蒿素和双氢青蒿素（结构如图）的下列说法，错误的是（　　）A．青蒿素的分子式为C15H22O5B．由青蒿素制备双氢青蒿素的反应属还原反应C．青蒿素分子中含有过氧键和酯基、醚键D．双氢青蒿素分子中有2个六元环和2个七元环