1. At some point the murderers turned to Mary, pointing a pistol at her heavily pregnant belly.

解析：這是一個(gè)含有現(xiàn)在分詞短語的復(fù)合句。

主句是：At some point the murderers turned to Mary，現(xiàn)在分詞短語是：pointing a pistol at her heavily pregnant belly。

在主句中at some point是做時(shí)間狀語。現(xiàn)在分詞短語是做伴隨狀況狀語。

2. Instead of being reduced to a weeping wreck, Mary was strangely calm.

解析：這個(gè)句子是個(gè)簡單句。

其中的instead of being reduced to a weeping wreck是做狀語，其中的being reduced to a weeping wreck是動(dòng)名詞短語作介詞的賓語。

在動(dòng)名詞短語中，weeping是現(xiàn)在分詞作前置定語修飾名詞wreck。

3. On June 19th, at Edinburgh Castle, Mary gave birth to the boy who would become James VI of Scotland.

解析：這是一個(gè)含有定語從句的復(fù)合句。

主句是：On June 19th, at Edinburgh Castle, Mary gave birth to the boy，定于從句中從句是：who would become James VI of Scotland。

在主句中On June 19th做時(shí)間狀語，at Edinburgh Castle做地點(diǎn)狀語，主語當(dāng)時(shí)間狀語和地點(diǎn)狀語同時(shí)位于句首時(shí)，時(shí)間狀語在前，地點(diǎn)狀語在后。

在定于從句中，引導(dǎo)出的定于從句的關(guān)系代詞是who，先行詞是boy。先行詞在定于從句中做主語，是指人，所以關(guān)系代詞who和that都可以使用。由于是做主語，不可省略這個(gè)關(guān)系代詞。

4. On hearing the news, Elizabeth's reaction was to cry, “Alack, the Queen of Scots is lighter of a bonny son and I am but of barren stock.”

解析：這個(gè)句子中的on hearing something這個(gè)結(jié)構(gòu)表示“一聽到......馬上就.......”，做時(shí)間狀語。