老的筛管无输导能力，主要是由于其内产生了（）。
A、侵填体
B、胼胝体
C、原生质体
D、造粉体
参考答案：B
正常人体细胞染色体的数目是（）
A.20对
B.22对
C.23对
D.25条
E.28条
An investor has the following assets: $ 5000 in bonds with an expected return of 8%. $ 10000 in equities with an expected return of 12%. $ 5000 in real estate with an expected return of 10%. What is the portfolio's expected return（）
A. 10.00%.
B. 10.75%.
C. 10.50%.
