Select all the correct answers.

A particular plant has two alleles that control the length of its stem. [tex]$T$[/tex] represents the dominant allele that codes for a tall stem, and [tex]$t$[/tex] represents the recessive allele that codes for a short stem. Based on the Punnett squares, which two statements are true about the genotype of the plant's stem length?

\begin{tabular}{|c|c|c|}
\hline First Generation & [tex]$t$[/tex] & [tex]$t$[/tex] \\
\hline [tex]$T$[/tex] & [tex]$Tt$[/tex] & [tex]$Tt$[/tex] \\
\hline [tex]$T$[/tex] & [tex]$Tt$[/tex] & [tex]$Tt$[/tex] \\
\hline
\end{tabular}

\begin{tabular}{|c|c|c|}
\hline Second Generation & [tex]$T$[/tex] & [tex]$t$[/tex] \\
\hline [tex]$T$[/tex] & [tex]$TT$[/tex] & [tex]$Tt$[/tex] \\
\hline [tex]$t$[/tex] & [tex]$Tt$[/tex] & [tex]$tt$[/tex] \\
\hline
\end{tabular}

A. Plants with short stems are homozygous for that trait.
B. Plants with tall stems are always homozygous for that trait.
C. Both parent plants in the second generation are heterozygous.
D. Both parent plants in the second generation are homozygous.

To determine the correct answers, let's go through each statement carefully and analyze the genotypes using the information provided by the Punnett squares.

### First Generation Punnett Square:
```
│ t │ t
────┼────┼────
T │ Tt │ Tt
────┼────┼────
T │ Tt │ Tt
```
### Second Generation Punnett Square:
```
│ T │ t
────┼────┼────
T │ TT │ Tt
────┼────┼────
t │ Tt │ tt
```

### Analysis of the Statements:
1. Plants with short stems are homozygous for that trait.
- Short stems are coded by the recessive allele 't'. For a plant to have short stems, its genotype must be 'tt'. This means it must have two copies of the recessive allele, which makes it homozygous recessive.
- Therefore, this statement is true.

2. Plants with tall stems are always homozygous for that trait.
- Tall stems are coded by the dominant allele 'T'. A plant can be tall if its genotype is either 'TT' (homozygous dominant) or 'Tt' (heterozygous).
- Since a heterozygous genotype can also result in a tall stem, this statement is false.

3. Both parent plants in second generation are heterozygous.
- If we refer to the second-generation Punnett square, we can see that the parents' genotypes can be 'TT', 'Tt', or 'tt'. The parents in this case seem to produce 'TT', 'Tt', 'Tt', and 'tt'. If either of them were homozygous, they would not produce these genotypes.
- If we consider that two of the offspring are 'Tt', it indicates at least one parent is 'Tt'. The parents can be 'Tt' x 'Tt' combination but not definitely 'both heterozygous'. Since the question is ambiguous about specifics fully disqualifying mixed pairs like 'Tt x TT', the statement is false.

4. Both parent plants in second generation are homozygous.
- For the second-generation cross to produce a 'TT', 'Tt', 'Tt', and 'tt' set of offspring, the parents must be homozygous dominant 'TT' and homozygous recessive 'tt'.
- Therefore, this statement is true.

### Correct Answers:
- Statement 1: Plants with short stems are homozygous for that trait.
- Statement 4: Both parent plants in second generation are homozygous.

Thus, the correct answers are the statements numbered 1 and 4.