Henry can’t attend the party ----- at Tom’s house at present

Henry can’t attend the party _____ at Tom’s house at present because he is preparing the speech at the party _____ at Marie’s house tomorrow.
选项:a、held/being held b、to be held/to be held c、 to be held/ held
d、 being held/to be held
为什么选D?请分析并翻译整句