How much of his speech do you think you have understood— . I wish I had worked harder.

Li Na plays ________ tennis very well. She has become ____first Asianwoman to reach a Grand Slam(大满贯) final.

－What’s Tom doing now－He in the library.

填入下面一段文字横线处的语句，最恰当的一句是（ ）前沿科学已经逐渐解开了人类衰老及长寿的密码，这个密码便是存在于染色体上 “端粒”。端粒保护着染色体，就像鞋带两头的塑料封套保证鞋带不会松牙一样。当细胞常分裂时，细胞中的染色体会跟着复制，形成新的配对, 。但是端粒自身也有命。细胞每分裂一次，端粒就缩短一次，当端粒不能再缩短时，细胞就无法继续分裂而亡。可以说，端粒的长度决定着生命的寿命。

My brother ____ from Monday to Friday.